If you're mainly looking to get the large bolt pattern, and already have, or can get the '71 B-body parts inexpensively, it's a pretty good way to go.
If I were going to drive the car hard at all, I'd always thinking about those ball joint spacers, and wondering if I just shouldn't have just got the new control arms with the bigger ball joint. They made them bigger for a reason, and for a little more you get new control arms with zero road fatigue, and with new ball joints and bushings. I've never heard of a failure with the spacers, and I'm sure Dr Diff would never sell anything suspect, but that's just what I would do.
Mopar Upper Control Arms
One other consideration is that the B-body rotors are a little pricey. We've gotten used to cheap rotors, but I haven't found many for this application. Rock Auto shows one Centric rotor in stock at $51.79, then they go to $100+ at Summit, NAPA, etc.
Pads and rotors for the original '69 Kelsey-Hayes discs are available at pretty good prices at the moment. Because they are also used by Mustangs of the era, pads are generally always available. I've found rotor availability to be spotty over the past few years, however. After being disco'd for several years, the rear drums for the '69 are available again. Centric 12363044 are reasonably priced at Summit and Rock Auto. If you're planning using re-drilled axles for the large bolt pattern rear, you may want to grab some of these while you can.
Good luck with your project!
