Link has everything you need to know. Get the 73-76 A-body spindles
http://www.moparaction.com/tech/archive/disc-main.html
Except that there is absolutely nothing wrong with using F/M/J spindles. They're in every junk yard, and work just fine. The bit about "over-angling" the ball joints is complete and total BS. In fact, there's a strong argument that using F/M/J spindles has a positive effect, especially for those using wider tires with more modern compounds- they improve the camber gain of the suspension.
Don't take my word for it...
http://www.moparmusclemagazine.com/techarticles/suspension/mopp_0503_swapping_a_and_b_disc_brake_spindles/Ehrenburg just hates everything not perfectly stock. Brake hose routing issues? Give me a break. Just use the hoses from the later cars, which rear-mounted the disks. Bill Reilly wrote the second article showing the F/M/J spindles are just fine, he knows more than a few things about suspension geometry, given that he designed the AlterKation suspension.
Doesn't your '73 Cuda already have disk brakes? If it does, all you need to upgrade to 11 3/4" rotors on the front are new caliper brackets. Do you have pin or slider style calipers? If you've got sliders, you can buy the 11 3/4" caliper brackets from Dr. Diff. If you've got the pin style, shoot me a PM. I have some 11 3/4" pin style caliper brackets that will let you bolt on a set of 11 3/4" rotors. Nice braking upgrade without even changing the calipers.
