It's generally uneconomical to buy a whole bike's worth of vintage parts off ebay for a bare frame that's been previously parted out. You'd spend much more than the finished complete bike is worth. That's why people part out bikes. (unfortunately - in my view)

One option could be to collect vintage components over time and as you find them at a decent price. This approach requires you to forget the whole notion of groupsets. Instead, find quality components that are appropriate to the bike. For example: Sugino Mighty crank, Cyclone derailleurs, Gran Compe brakes, etc. Velocity SunM13 wheelsets are perfectly fine. I'd much rather see a bike like this with an assortment of top shelf components than a mid range 'groupset' that's all matchy matchy. Mid range isn't really right for this bike.

Alternatively, simply get yourself a modern Ultegra group, and some sort of wheels, bolt 'em on, and call it a day. That's probably what I would do in this particular case.

While yes, you can get away with simply jamming 130 wheels into a 126mm frame, it's much better to properly realign it. Not that hard really. Look up Sheldon Brown's instructions.

EDIT: On second thought Suntour sprint would be fine, if you can find a whole group of it somehow. It came out a few years later than this bike, FWIW. It was an Ultegra competitor but Ultegra has been upgraded since then. In the 80s it was mid level to upper mid level. (arguably)