I've updated a 1981 Raleigh Arena to a 3x9 speed 105 groupset - it worked well, though there were some gotchas.
I was lucky enough to get a donor bike with a working groupset but a damaged frame. So the entry costs were low.
The wheels I already had, which were common 622 size. The frame used to have 630 wheels, so the modern brake calipers didn't reach and I had to buy brand new long-reach dual pivots from Tektro, their R559 model:
Other info on brakes Caliper drop for bike conversion and How do I know if I can replace the 27 inch wheels with 700c wheels on my bike?
The groupset went on just like normal - the rear dropouts need some pressure to separate them and let the axle in, but it was never cold-set. However the frame had been damaged in a seat stay in the past, so could have been off.
Later shot with less fragile wheels: