I have a 74 Nova clip under my 52 1/2 ton.I don't know if there is a difference in 75.The front wheels are Chev rally rims,7"wide 4" backspace.If I turn the wheels in a tight turn with two people in the cab the tires do rub on the fenders.Tires are 205R/65/15
The rear end is a 10 bolt out of the same Nova.Rims are Rally's 8" 41/2" backspace,tires 245R/60/15.The tires were real close to the box sides so a 1/2"spacer was used.Sorry I don't know the actual widths of the front or the rearends
Hope this helps you
Boyd