Unfortunately, that doesn't divulge the year of the bike.

Pinning down the year(s) of production will help identify compatible parts:
Serial numbers of the two frames may help identify the year each was manufactured.
Any tube designations (such as "cadre allege" or "Carbolite 103" may also help -- the years for use of those tubesets are known.

Another method is to search for Peugeot catalogs for various years, and find examples that match. Here's a good site:
https://www.bikeboompeugeot.com
and in particular:
https://www.bikeboompeugeot.com/Broc...ures%20USA.htm
Your white bike looks like it might be a 1974 model, check out the UO18 (or the UE18). Colors aren't listed.
https://www.bikeboompeugeot.com/Broc...20Page%209.jpg
https://www.bikeboompeugeot.com/Broc...20Page%205.jpg
While the silver frame could be from 1980, where there's a "Grand Sport" mixte:
https://www.bikeboompeugeot.com/Broc...re%20UO19C.jpg

The white one might say "Tour du Monde" or more likely "Record du Monde". The silver frame has a plate for mounting the rear brake, which is not as classy as the tube found on the white. Obviously the silver frame is in better cosmetic shape; but whatever you do, either keep the white frame with a view to refinishing it (not necessarily, but possibly, with a full complement of replacement decals and lug striping), or else sell it to someone who has an interest in doing that!

As far as transfer of components between the two frames, this might turn out to be fairly easy, or it might end up, at least to some extent, in a hair-pulling exercise, due to changes in design, sizing, improvements between the two different years.

Peugeot seatposts:
https://www.bikeforums.net/classic-v...-database.html
Sort of general, but it shows that a 24 mm seat post is not unreasonable for a bike(s) like yours. The silver one looks like the seat post opening may have been abraded or otherwise "mistreated" from its original state. Does the post, when inserted, say, 5" or so into the silver frame, seem particularly loose? If so, then that frame wants a larger post. It's hard to do these things with just a ruler; either you need a set of posts of known diameter, or else a dial or digital caliper, which will measure reliably to 10ths of a mm, and somewhat less reliably to hundredths. What's interesting is that in miamijim's seat post database, there's nothing between 24 and 26.4, though OLDYELLR's post #4 refers to Sutherland's, which lists about 5 sizes between them -- so I guess that the best policy is to find a reasonable post for whichever frame by empirical means: loose is bad, while if it doesn't fit easily, don't force it.

Sutherland's 6th edition is available here:
https://www.dropbox.com/s/qclnmckcer...206th.pdf?dl=0
Note that I've bookmarked it, but those only appear if using Bluebeam or Acrobat DC (free); Apple Preview seems to be Adobe-bookmark-challenged. The file has also been OCRed, so that you can do text searches; sometimes these fail in the 6th, because I got the original (unbookmarked, un-OCRed) PDF file from another source.
I also have Sutherland's 4th in the same format, but I don't find it helpful for much that the 6th doesn't cover equally well. I scanned this myself from a hard-copy that I own, so one thing that can be said for it is that the OCR was more successful. All that being said, I use the 6th myself almost exclusively.

The crankset on the white frame is "cottered" which is something that went out of use, generally, by the early 70s. You can read all about crankset standards and construction via Sheldon Brown. If the parts are undamaged, and will fit the silver frame, then there's no problem with that -- a lot of folks hereabouts have, like, and use cottered cranks. But if anything is amiss about them, then it might be cheaper and more practical to replace the crankset and bottom bracket (bearing unit that goes through the frame and to which the cranks are fastened) in toto. Before removing the crankset from the white frame, you should measure (within a mm is OK) the distance of one of the chainrings' teeth from the center of the bike frame (and keep track of which one it is) so that a reasonable substitute of the bottom bracket can be determined (this is "chainline". Also measure the width of the bottom bracket shell (painted) on both frames; probably the same, but could be different, and important for specifying a replacement. In any event, if the two BB shells aren't the same width and threading, you'll have some difficulty moving the white bike's cranks to the silver one. As to removing the white frame's cranks, I have no personal experience with cottered sets, but you should be able to find this on Sheldon Brown's site, and there are definitely wrong ways to do this, that result in a bent cotter, which is very bad. So be careful.

It surprises me that the handlebar stem is marked 22.2 mm; typically French bikes have a 22.0 mm stem -- one of their cardinal differences from bikes made almost everywhere else (22.2 mm being 7/8", which was the standard in England (where it started), the Low Countries, Italy. But if it's marked, and it fits both forks equally well (same criteria as for seatposts), no problem.

I don't see the top nut and threaded race for the headset, and the keyed washer and/or brake cable housing hanger that goes between them, but presume that you have them. The pressed on/in chromed headset parts on the two frames and forks may be identical, or at least compatible; but then again they may not, so you'd need to trial fit the top nut/race on the silver frame to verify if it will work acceptably. Look for "brinnelling" (indentations made by the bearing balls) in both lower races of each frame and it's fork -- that's where the real work and loading of the headset is done. The top bearing is just to establish clearance/fit and keep the fork centered on its proper axis. Generally these old chromed steel races are quite tough, but if ridden for a long time poorly adjusted they will suffer.

A final observation for now: It's unclear whether your main interest is in riding a bike (having your own that's functioning) or in having a bike project. Either is fine, but as someone who's less than highly experienced and tool-equipped, what seemed like a lark in the beginning may turn out to be a case of biting off more than one cares to chew. There's often a long road between a bike project and a functioning bike. I suggest that if you want to continue in the direction you've started, that you at least take the dispiriting "I don't have a bike to ride" pressure off of yourself by finding something that you can ride for awhile -- not the bike of your dreams, but one that will serve your purposes in the short or medium term. I am speaking from personal experience. I'm still perfectly willing to help you with technical issues going forward (though others here may have better knowledge for this case), but it's important to be practical.