Any year S10 works, as Old Iron said. There are 5 or 6 different wheelbases of S10/Blazer, and what you use depends on the wheelbase of what you're putting it under of course.
As OI said, a regular cab long box S10 is the right length for a regular cab short box vintage truck. On some body styles of vintage GM, the wheels weren't centered in the wheel wells, so you don't even need to move the axle because you can make up the difference by centering the wheels or you can give it the race car look by locating the rear wheels a bit rearward in the fenders.
The older the S10, generally you'll be able to use more components from the truck as a donor if you want to go that way and are starting from a mostly complete truck.
The benefits of the swap are that you get something that has suspension, brakes, and steering that were all designed to work together and you're not reinvent anything. There were also the ZQ8 S10s so if you want a more performance-oriented handling package those parts can be found as well. Mine handles really well, and I love the deep dish wheel look so that's another reason I like the swap. Last year I installed a larger front sway bar and a rear sway bar from a ZQ8 and I've got monotube shocks waiting to be installed.
You should note the S10 frame is too wide for some vintage cabs, so depending on what you're working on it may not work the best.
