Barrettscv 

I'm considering using Shimano 8-speed indexed 600 series downtube shifters with a 13-24 seven speed freewheel and a Shimano 7 & 8 speed XT rear derailleur.

Will in provide indexed shifting and work well?

masi61

"Negative" would be my best guess to your query. The rear freewheel isn't particularly consisted in its cog to cog spacing. Why not just rotate the adjustment ring on the down tube shifter to the friction setting?

Ex Pres 

off 0.2mm/shift.
adjust to accurate in the 4th cog, and the max misalignment at each end = 0.6mm
some say it's good enough.
I'd rather use 7s downtube 600 shifters

GrayJay

It would probably work better if you disassemble the freewheel and use callipers to measure all the existing cogs and spacers, then use sandpaper to lap the spacers thinner where needed in order to get them right for the 4.8mm c-c cog spacing that 8s shimano shifting was designed for. Using a 9 speed chain may also help since the space between the relatively wide suntour cogs will need to be reduced.

Sheldon Brown's Bicycle Frame and Cassette Spacing Crib Sheet

zukahn1 

I would say negative also your setup should work if you change the right downtube shifter a 7s Shimano with a slight glich between 3 and forth. Yet for this setup I would buy a 8s freehweel spaced for your Shimano stuff and space and redish slightly as needed to get everything to work nicely. Then maybe change you big or front chainring to get your desired gearing. Not very expensive $20 for the freewheel and $10 for the chainring. You can sell off the 7s speed winner here or Ebay for $25-30 bucks to cover most of the cost.

Barrettscv 

Thanks for the input. I'm currently using an 8 speed Shimano cassette with good results. However the rims need replacing. I have multiple sets of wheels with 126mms wide hubs for freewheel. I also have a 13-24 seven speed Suntour Winner freewheel. The logical thing to do is: switch to friction mode with the existing shifters, or install 7 speed indexed shifters. I like Suntour Barcons, so that's another option.

wrk101

Just use a Shimano 7 speed freewheel, they are available on line cheap. Limit out one end.

Barrettscv 

Is the cog spacing on the seven speed freewheel compatible with a 8-speed indexed shifter?

likebike23

The issue I see is that some of the 7 speed Suntour freewheels had variable spacing between cogs as Masi61 stated. You could use the link in Gray Jay's post to see what we're talking about. If the freewheel you have is variably spaced, you need to use an Accushift 7 speed setup if you want indexing. Wrk101's suggestion is very good as well, as the Shimano 7 speed freewheel is really close to the 8 speed spacing and would work pretty well. I think you've got enough good info here to get 'r done

zukahn1 

Yes but you will only get 7 and have to hard limit the shifter and rd to 7.

wrk101

Seven speed Shimano, near identical to Shimano 8 speed.

dddd

Either the Suntour or Shimano 7s freewheels would work if adjusted carefully, but as GrayJay mentioned a narrower nine-speed chain will make either freewheel's spacing mis-match more forgiving of the adjustment difficulty and of the degree of effort needed in moving the shift lever carefully while riding.

Some good-quality heat-shrink tubing over the length of cable that wraps around the shifter's spool will also effect a slightly-longer cable pull, which will likely be beneficial to either of these freewheels, particularly a Shimano freewheel.
You can find a (Shimano 7s-spaced) 7s Sunrace freewheel in 13-25t for less than $20 online, and it worked on my Campag Xenon Syncho 7s setup once I replaced the 7s chain with a 9s chain. With the 7s chain I could not achieve a satisfactory adjustment, but now it works extremely well.