I have a 68 with an original 10bolt and just bought a 9 inch salvaged from a versaille. I am about to buy new wheels (billet fastlanes) and was wondering what backspacing I should get. The new axle measures 52.5" flange to flange and ~58.25" from mounting surface outside the rotors. Would the standard 5.5" backspacing on a 17x9.5 wheel work or do i need to change to 4.5" backspacing to account for the axle swap??

Thanks

60.25" for a stock rear and you're at 58.25 so 2" O/A shorter and I will guess stock wheelwells :confused:
1" per side = 3.5" backspace since 4.5" is the norm (w/ 15"wheels).
When plus sizing to 16"+ wheels most go to 5.5" so your 4.5" "should" be right.

Doug, thanks so much. They are stock wheel wells just wanted to get a second opinion before having the wheels built! Thanks.

I would measure to be 100% if I was having wheels "built".

My 68 has a 9" rear and is 59 or 59.5" IIRC, 17x9 rear wheels, 5" backspace, still needed a 3/8" spacer making it an effective 4-5/8" backspace to keep from rubbing on the inside with a 255/50/17 rear tire.