widest tire with spring relocation

-- Yep ! That's what I did. -- BUT-- I thought that the kit was 3/4". - Probably not a big deal - Also, I had 15" X 8" Mopar Steel wheels, with altered back spacing. - Don't remember the BS.
I have 255/60 r15's on the rear of my 70 Dart, with 8.75 rear n small bolts...

But I had relocated the spring perches in 3/4 inches (which only gives u like 1/2 inch more room), and also had 5 1/8 backspaced steel wheels made, so it is centered nicely. I can actually fit 275/60 r15's now very easy with plenty of room to spare...

The fronts are 215/65 r 15's to fit well up front turning-wise...