Don't count on stem or seat post fitting. It really depends on the era of the bike, and more. BB may or may not be correct. Raleigh for example had their own standard, which was different than the british standard. And then you have rear wheel spacing. Those changed significantly over the years, from 120mm to 126mm to 130mm to 135mm. Some of the british bikes used smaller diameter front axles too.

Still I continue to find all the parts I need in the form of complete bikes. But often, it just isn't ONE bike. Picked up two today, one made in USA, one made in Japan. Different stem ODs, different seat post ODs, different rear wheel spacing, different headset specs, different wheel OD, on and on.

I can't imagine a 1970s cottered crank Raleigh Gran Prix frame having ANY value. Generally, I target 1980s made in Japan bikes, that tended to use standardized stuff. One I picked up today is a good example. 1985 made in Japan Nishiki, almost all Shimano 600 parts. Frame alone should more than cover cost, but it was a high end model back in the day.