For overall looks and handling I prefer 15 x 7 with 235/75R15. The 15 x 8 wheels might interfere with the suspension and the 70 series tires might alter your overall gear ratio, lowing it.
Since you posted your question in the '60-66 topic I would assume that your truck falls within that year range, therefore it most likely does not have power steering and gearing that would be normal for 670 x 15 tires, which are in the 28" range, very close to the 235/75R15 tires.
I have 235/75R15 on 5 lug alloy wheels on 3.42 10 bolt GM rear end in my '64 C10, trk drives great. Wm.
