Another Wheel/tire question. Please help

[CC69Rat]

You may already know, but just trying to help.

The earlier trucks (67 - mid 1970) have a little more narrow rear axle housing than the later trucks. 1970 was the transition year. I guess the assembly line just used up what they had available. I have seen 1970 model trucks with either, the narrow or wider axle housing.

I say that to say.. you will want to measure the axle housing in your truck now unless you are 100% sure it is the original housing. Chances are it is but just saying we never know. I have seen wide 6 lug housings. They're out there..

The early housing is 55.5" long if you measure from the inside of one brake backing plate over to the other side in the same place. The late housing will be 57" long.

If by some chance you have the late housing, it will impact your backspacing. Kinda leading into my answer to your question.

I run 295/45r20 on a 20x10 with 5" BS. Stock length narrow housing. I change to 5.5" BS on trucks with the wider housing. But it's a 10in wheel. You're looking at a 20x9.5 with 5.25" BS so you're right there in that sweet spot, in my opinion. 4.5/6.5 drop on this truck.

255/45 with 20x8.5 wheel. 4 5/8" BS
295/45 with a 20x10 wheel. 5" BS.

With the wheels youre looking at, youd be .25" from these measurements. Side by side. ope this helps.