Having done two 1973-76 A body disc brake swaps onto 1966 down cars; it's 99% plug 'n' play using the upper control arms/lower ball joints from the donor vehicle along with a matching 5 on 4.5" rear end. The only modifications I had to make were installing different brake tubing nuts to match up...
For the record: IF we're going to squabble over non factory mods on an A body; then it should be 'illegal' to install a 1967 up dual chamber drum brake master cylinder onto a 1966 down model with the same size drums...........
Another modification could be 3 point seatbelts since the B pillars...
Having personally done two 1973+ A body disc brake swaps onto narrow bodies; I had no bump steer issues at all, maybe because I kept the Torsion bars at stock height. :)
Many years ago while still stuck living in the Wash DC area I had a 1967 Dodge Dart 4 door with the following options:
273-2V
AT
PS
manual disc brakes
14" tires
HD suspension with a front sway bar
factory AC
silver body with a black vinyl roof and red cloth interior
AM radio
remote controlled...
Unless the OP is dead set on keeping his 1966 Dart 100% original; I'd install a 1967-78 Dart/Aspen manual disc brake cylinder with matching proportioning valve/hard lines and call it a day. The firewall 'footprint' and pushrod are identical. Note; I've done two drum to disc swaps on 1966 down A...
Long story short: I had a 1994 Dodge Caravan SWB with a 3.3L V6 and was extremely impressed with it with its bulletproof reliability, performance and MPG.
Does anybody have any idea if fitting a 3.3L from an Intrepid or similar be feasible assuming there is a tranny that will bolt up so I...
I believe all 1962-72 drum brake A bodies all used the same upper and lower ball joints. Supposedly; the same years disc brake lower joints will work as well on drum brake spindles but are stronger.