At the rear of the car, just aft and outboard of the forward leaf spring eye is a flanged oval shaped hole. Drop a plum-bob from this point and again, mark the spot on the floor.
[roadbike, mountain bike and downhill bike gathering dust in the background....they hate me]
Once you have your marks you then measure diagonally between the marks (left-rear to right-front & right-rear to left-front). The values are sure to be different at first which is why I left the body bushing bolts hand-tight above. You'll have to bump, tweak and nudge the subframe around until the measurements are close to or equal. It'll take a few times to get it right but be patient and make small adjustments. Mine came out exactly equal at 90 1/16" from corner to corner.
I compared this to the measurements I took when I disassembled the car. The factory left the differential at 90 3/16" and 89 15/16". A 1/4" out of square condition. I guess that too explains the disparate alignment shim stacks.
I left the bushing at the Core Support hand tight to allow me to nudge it around when I put the bodywork back on the car at a later date.
Next step will be the installation of the DSE subframe connectors. I'm starting on that tonight so we should have at least a preliminary update to this thread in a few days.