Will these fit under a '71 Chevelle with no mods? Or am I limited to 5.5 backspace?

I'm unsure if mine are 4 or 4.5 but I'm guessing you need at least 5 in backspace without mods, and its not gonna fit a wider tire without 5.5

i might be wrong, but i doubt it

I was curious b/c I was thinking on placing a bid for some 15X10 draglites I saw on ebay.

you need minimum 5" to clear but 5.5" is ideal for 15x10's with a stock width rear.