you can run 15 x 8.5s with a standard diff width on HQ-WB on rears...

ask for 4. 7/8th inch back space. 4.3/4 backspace would probably fit too. and i haven't tried yet, but 4.5 inch backspace may work as well....

if you wanna go VN + up diff, remember to get the commodore tailshaft so you can use the flange set up on your tailshaft conversion.