Front and rear steelie wheels with airride??

[HSRACER]

So i have some steel wheels on my 67 but they are 3 different backspacing from previous owner. None make any sense from a fitment standpoint. All have 1/4 inch spacers. They are all 15 inch steels but 2 have 4.5 back spacing 1 has 4 inch and the other has 3.75.

On steel 15 inch wheels, what backspacing and wheel width can be run with airride, stock front spindles, control arms and stock rear axle width that will allow for maximum placement of the tires?

In other words,I want the rear tires to just barely clear the outer lips of the rear fenders and the front to just barely clear the LCA and the tierod ends so when I drop it there are no issues.

I have stock full wheel hubcaps i am trying to keep and would also like to loose the spacers. Thanks in advance.