I don't know about mountain bikes or modern carbon fiber marvels, but older "steelie" road bikes are amazingly upgradeable. The only thing that stops you from

I don't know about mountain bikes or modern carbon fiber marvels, but older "steelie" road bikes are amazingly upgradeable. The only thing that stops you from putting in a modern 11-speed compatible wheel is that the axle is 4mm longer, but that can be accommodated by "respacing" the frame. I've done it on one of my bikes, was a bit scary to do (you have to bend it out a lot more than 4mm to have it settle back to the right spacing) but in the end, easy. You'll have to keep the rim brakes, obviously, and front derailers aren't very standardized. But the rest of the drivetrain, right up to modern outboard bearing crank sets, will fit your 35 year old frame just fine. The cheap "MicroNew" shifters from Ali Express, while not as pretty as high end Shimano stuff, work fine - I've put a few thousand kilometers on the 7-speed and 8-speed version so far and they're comfortable and reliable if a bit "clicky". Modern stems and handlebars can be fitted to your old fork by inserting one of those quill/threadless adapters. All done with not much attention to weight, my modernized steel bikes weigh in around 12kg, which is heavy by carbon fiber standards, but not too bad.