Depends, IMHO. Different truck in a lot of aspects. Hydraulic clutch, torsion bar front suspension instead of coil springs, 10 bolt rear end, etc. If it's a good low mileage truck, though, you may not really need any major parts, which will be the hard to find stuff. Small stuff seems to be easily available through all the truck parts places.
-I don't have one though, so take this info for what it is. (Hey, remember that "worth what you paid for it" thing? He He.)
Some of my crap:
1963 C-30 flatbed dually 292/SM420
1965 C-10 LWB fleet 250/column shift 3 speed
1965 C-30 9' stepside 250/SM420/4.10 gears (my DD)
Website I made for my crap:
http://www.66submarine.com