I put 235/70-15s on 8-inch wheels on my '55 1st suburban, which should be similiar enough to yours.
I did that a week or two after I bought it, while it was still six-lug all the way around. I've since changed it to five-lug, but still run the same size wheel and tire, just a different bolt pattern.
This isn't the right answer if you want a stock look.
