On the 64-70 somethin a-bodys, the spindles and brakes all interchange along with other stuff. The disc brake kits are anywhere from $700 to infinity and beyond. I didnt switch over to discs,the $150, I just replaced the tie rods/ends, a-arm bushings, balljoints, brake pads and some dirt cheap shocks.
Just thinking here, mabey if you find a set of spindles that match yours on the 48 from a donor vehicle with discs it could work just a swap. But finding out which ones are pretty much the same will be tricky. The corvette, you say it looks like its similar it could possibly interchange....anything can be made to work just how much work is the question
If they make a kit for it, I would go that way if money isnt tight.
Also alot less hassle to go through I assume using a kit.
I was looking on google for the suspension of the 48 fleetline, i didnt come up with any but i did come across a lowrider magazine article where this dude had air ride tech kit on it. That could be another option also. Not sayin pimp it out or nothin but air does make it nice to have adjustable height.