Ok I looked up the DC Performance Book under Tech Tip #5 Rally Preparation PN P4120595. Here is a synopsis of what they write there...

Section 7 " 4 1/2" Bolt Circle Wheels -page 153

It says here to use PN 2836148 special rotor-hub assembly with all wheel studs 1/2-20 right hand threads. Also says there was a special axle for an A-body 8 3/4 with 4 1/2" bolt circle and all 1/2-20 right hand threads. That PN is 2513750-M and 2513751-M. And that the brake drum must be replaced with PN 2534173. It also says the same brake shoes from the SBP drums can be used. Which to me means those are weird special drums because A-bodies uses a unique width shoe I thought?

Section 8 Wheels pg 154

It says to use 14x6 Crager rims with SBP. Also suggests American Racing 15x7 work well but use the special hub and rotor assemblies noted in Section 7.

-Ok, that's one source. That doesn't 100% eliminate the possibility of 15x7 steel SBP rims. Next would be some old Chrysler aftermarket performance catalogs like this: http://www.hamtramck-historical.com/1968Hi-PoParts-01.shtml