Thank you all for sharing the info here.

I've not seen or heard of any definative info on whether large bolt pattern hubs were developed before '68. We see plenty of photos of '66 Trans-Am cars using aftermarket rims in the later races, but they could have been SBP or BBP. I agree it seems possible, and it may or may not have been a special run or a remachined part from another application.

The Part Number for the special 4 1/2" bolt circle hub-rotor was 2836148.
"The same bearings and seal are used and all wheel studs are 1/2-20 right-hand thread."

"The rear axle shafts..[ for 8 3/4"]...may be replaced with special axle shafts with 4 1/2" bolt circle for wheel mounting, P.N. 2513750-M and 2513751-M. All wheel studs are 1/2-20 right-hand thread. The brake drums must also be replaced with P.N. 2534173. The same brake shoes, etc. may be used."

from "Rally Preperation" in Mopar Chassis, Carroll Shelby Speed Secrets: Direct Connection Suspension Modifications... Chrysler Corp. Part No. P4349341 (1984) page 53.

Anyone know when the rally bulletin was first released? It had to be long before 1984. By '84 there's a note that the large bolt pattern 8.75" axles mentioned are no longer available.