[Captainfab]

Because your truck is a C20, you will have to switch the entire crossmember. The '63-'66 C20's use a flat lower control arm shaft, that bolts flat to the crossmember. The C10's from '63 and up, use a round lower control arm shaft, which sit in saddles that are riveted to the crossmember. Your C20 crossmember does not have those saddles to accomodate the C10 lower control arm shafts. Yes you could weld some saddles to your C20 crossmember, but you would have to be very precise in doing so, as they have to be in an exact location. IMO it would just be easier to change the entire crossmember.