[Bad70sbchevy]

Hi all, was looking on getting some 18" rims on my 1970 c-10. Currently I'm in the process of converting it over to disk brakes front and back, swapping to a 5x4.75 bolt pattern, and a 2.5" drop spindle with 4" drop coil springs in the rear. With that said I'm looking at running the following tire combo:

18x8 with 275/40r18 with 4.5" backspacing fronts
18x10 with 295/40r18 with 5.75" rear

I think the front combo will work, but how about the rear? It is a fleetside, but was curious if I had to run a custom backspacing (looking at torq thrust IIs) to get them to fit or not as I'm currently running 15x10 all around with 4" backspacing.

Axle is the stock 12in btw.