Rear axle/brake Q's?

I have a 67 valiant, with 8 3/4" rear that was installed by the guy I bought it from. He had completed a BBP axle swap. But I don't know the details on how he did it, (new axles, modified axles). Because he still has the SBP brake drums, just redrilled to BBP.

Can someone please provide the BBP axle length/offset for 10"x1.75" drums, and also for 10"x2.5" drums? I want to compare what I have, to what it should be.

I just pulled the axles to replace the bearings, and am discovering all the "interesting" work the guy had done on this car.