if you want to go with pre-made, there is a guy on ebay (not cosmo) selling the tarozzi rearsets and occasionally he has them for cb750s. About the same quality as raask (ok, slightly better) and the price is better. I recommend them over the raask because on some models (69-76 K) the raask rearsets are mounted a little too high. Tarozzi's will be more comfortable.
If you are 6'5"-ish like me you could probably get away with a set of generic rearsets (like tarozzi) mounted through the passenger peg mount.