[Schurkey]

I guess I don't understand what's going on.

You're mounting the engine with a mid-plate. This pushes the transmission rearward by the thickness of that mid-plate.

The transmission has a slip-yoke at the rear for the driveshaft connection. The rearward transmission causes the splines to engage more deeply.

None of which changes the location of the axle. The axle doesn't move when the transmission is crammed rearward so long as the output shaft/driveshaft yoke splines don't bottom out.

So to my thinking, you have no reason to adjust the axle-locating linkage. The "answer" is "zero half-turns".

You MIGHT have reason to shorten the driveshaft by the amount the transmission is moved rearward.

Am I wrong? Not understanding something everyone else "gets"?