273's answer is exactly right. Yes, they will bolt to the frame, but there are other issues. As he said, the UCA's do not directly interchange. The ball joint is bigger and only fits a 73+ spindle. Many swap all 73+ parts to get "BBP disk brakes" (search that). Steering linkage also changed in 73+. Probably no issue using 63 steering w/ 73+ wheel parts (many have), but I recall some discussion of potential "bump steer".