How do I convert from single to dual master cylinder?

$250!
I converted my 64 & 65 to dual MC real cheaper. On both, I used a later Mopar MC (95-99 Breeze, Cirrus, Stratus). The 64 I kept manual and used a 2-4 bolt adapter plate ($30 ebay). The 65 I put the whole MC/Booster on 74 Valiant brackets (junkyard).

Re plumbing, can re-use your distribution block by 1/4 to 3/16 dbl-flare adapter in top port, 3/16 dbl-flare plug in rear port. I plumbed to my rear tube w/ a 3/16 dbl-flare union (all in Autozone bubble packs). I also plumbed an adj prop valve in my rear line in case I later change to front disks.