Caliper

Being a 1984, was this originally a frame made for 27x1 1/4" tires? If so, you can probably fit 700x35-37 tires in there due to the slightly smaller diameter rim of the 700c setup. Your limiting factor will likely be the chainstays. Also, find as wide a 700c rim as you can. The wider rim will plump up the tire and keep the rummer from flopping around with those wide tires for one, but also keep the braking surfaces further outboard, which helps with clearance for brake calipers. If your rim is super narrow (classic road rims) then the wide tire will end up in a "lightbulb" shape that may hit the caliper arms, as well as not being so stable for cornering. An internal rim width in the low 20's would be ideal, but those are getting hard to find for rim brakes it seems.

If you've got DT shifter brazeons on the frame and have brifters in your parts stash (or are willing to buy some old shifters from eBay) then you can get cable ends from several sources that will bolt on where the DT levers used to go. I've done this on four bikes and it works great. Modern or classic brifters and drivetrain and a classic frame play just fine together. I suppose the old stem shifters already come with a DT cable stop, so that would work fine as well.

Naturally, this all depends on what you call "gravel". If you are talking about riding dirt and gravel roads traveled by cars, you'll be fine. If you are thinking of using the bike as a rigid, drop bar MTB on gnarly singletrack then you will likely be disappointed.