Yes, ive run a 800 primary on a 750 and visa versa.
lf i where in your shoes and had a 72 750 with bender quads and a 800 primary, i would leave the 800 primary as is and try
lt. A 92 750 with benders tuned properly probably puts out about around the same HP as a 800,it may not deliver it in exactly the same way/place. You may get close with the stock 800 primary, if i wasn't happy or thought there was more power on the table i would then try a aftermarket spring setup for a stock 800.
Tough call, lot of variables, tuning, wear, riding conditions etc...................
Good luck