You can upgrade the front end to disc brakes by using the front crossmember from a 1072 - 1987 chevy pickup or a 1972-1991 suburban.....which is what I used on my 66 gmc pickup....91 burb....
the rear axle flanges can be redrilled for 5 lug for not a lot of money which is what I did on mine. be careful, I bought some 5 lug crgars for my truck before I realized that the truck 5 lug wheels are 5 x 5 pattern and the car 5 lug chevy that I had were 5 x 4-3/4, I ended up redrilling the front and rear hubs to accomodate the wheels (I got a really good deal on them and it was cheaper to redrill the hubs than to change the wheels. Go here is you want to see the build and the drilling of the rear axle flanges......
www.kieth.smugmug.com Kieth
oh yes go to the 66 gmc gallery.....