I would personally restore the amp to stock first, w. Master & pull boost. After that, let the owner give it a thorough test.
One thing that changed alot was the wiring dress. Having tried converting a later MV Bassman to an AB165 once, I learned the hard way that an improperly located ground wire can cause issues. I say this to caution against simply wiring to AB763, and make sure you follow the layout also, preferably by looking at an actual unmodded AB763 Twin Reverb.
Good luck, hope all goes well!