Originally an auto? hmmm somehow an auto in a 65 GMC doesn't fit right in my mind...probably just me...If it has a V8 and so on, I would definantly look into a front end sway. Disc Brakes should stop your son....well at least better then drums.
Bolt on IFS from 63-87

try that one for a rough idea of an easy (compared to the rest) disc swap. Good luck!