72 Dart, mini tub, narrow rear, spring relocation... Need tire wheel info

Ill try to answer these.

Sometimes people run into clearance issues when moving the rear back with the fuel tank.

What I suggest is to do the mini tub and spring relocation. Then get the wheels and tires centered in the well. Measure from back face to back face then you know your over all width. Trying to reach for numbers without measuring could result in error.

You have SS springs and you also have XHD springs. Both will offer a stiffer ride.

My Rear is 50 5/8 with thats a 15x10 wheel with 4.5 BS. Mine is mini tubed and springs relocated with using the SS springs.