47-55.1 Brake rotor conundrum

[51 3600]

Who knew that buying rear brake rotors could to be a major headache!
Without going into the long background story I'll start with what I was told many months ago. The rear axle on my '51 3600 is "from a '02 Z28 Camaro...well really a Transam". So I ordered a pair of rotors from Rock Auto and found they didn't fit. Rotor was jam up against the backing plate, disc was too thick to fit in the caliper and wheel lugs barely protruded through the rotor.



Checked with person in the know about the axle. "On second thought, I think instead we mounted a 2000 Blazer 4WD drive axle." Ok. Ordered a pair of Blazer rotors from RA. They didn't fit either. Disc fit in caliper but rotor was too deep just like the Camaro rotors and tight up against the backing plate. "Maybe a RWD?" Got smart this time and went to Auto Zone and bought one rotor to try. Doesn't fit. Disc thickness ok but still jammed up against backing plate and rotor about 1/4" away from the axle flange while still up against the backing plate.



So now I've spent a bunch of hours on the internet trying to figure out what I've got. Not being a mechanic doesn't help interpreting a lot of what I researched. A little of what I've learned:

Diff is Borg Warner 9 bolt used on 3rd gen F bodies. 3.27 gear ratio.



Calipers came with this axle and seem to fit fine but don't look like Camaro calipers at all and are similar but bigger than Blazer caliper pics I can find. One comment I found said Blazer 4WD calipers mount forward of axle and RWD ones mount rearward.


Other misc. info:
Backing plate to backing plate dimension of axle is 57.25"
Axle flange to axle flange dimension is 61.75" which would make wms to wms approximately 62.25".
Camaro rotor measures 2.375" from back surface of disc to inside of rotor wms surface. That dimension can't be bigger than 1.75" in order to fit on my axle and work with the caliper.

Sure could use some help from the wise counsel found on this forum. What have I got? Sorry this is so long. As Mark Twain said "If I had more time, I could make this shorter."