i don't think you need to change spindles just find the right brackets to bolt up. my 59 didnt need new spindles just adapter brackets shouldn't be to hard to find
'68 big Chebbys were available with front discs, as were all of the big GM cars of that day. Not sure what you would need to swap over, but a good knowledgeable salvage yard guy could help you. You might need a different master cylinder as well.
Found a deal on a set that has everything but the master cyl and booster including drilled and slotted rotors and stainless braided lines for $385. That would give me NEW everything and all in one box. I like new and I like all in one box!
Equalizer valve is different, too! I'd get all new SS lines, and braided lines to replace the rubber - a littlemore, but well worth it, IMO!
From what a buddy said while searching boneyards for parts to do this to a 68 Caprice, 68-69-70 fullsize Chevy would work, could not use any BOP or Caddy stuff as the ball joints were somehow different. Maybe 67 too, but rare? Heck, even back then those setups were rare. He eventually peiced it together from 3 69 parts cars and had to buy new rotors. 10-12 years back out here in SoCal, where there are still lots of these cars. I think the spindle/brake portion cost him more than you quoted above and the stuff was heavily used. Good luck, Tom