The mini tub is not hard at all. Just takes time is all. I have a 70 dart, mini tubbed, fender lip is not rolled. 15x10 with 4.5 back spacing. 325-50-15 leaves about 3/4 inch on both sides of the tire. However my rear end is narrowed.
I just finished the same thing. MT ET street radials 325/50/15 on 10 inch rims with 4 1/2 inches of back spacing. With lips cut off of frame rails and tubs welded flat against the frame you'll have about 3/4 inch on both sides of the tire.
Rear 325/50/15 MT ET STreet radials, 10 inch wheel with 4 1/2 back space.
Front MT 6 x 15 skinnier on 4 inch wheel with 1 3/4 backspace
Mini tubbed with RMS Street Lynks 4 link.