Rat Rod = deliberately crude. Often with mismatched parts and no flow or continuity.
In answer to the question, I'd run a rear end that matched the engine and trans. Pr Probably a 3.08 to 3.55 Gear ratio.
I run a Nova rear end from somewhere in the early 70's in my truck behind the 250 and 3 speed stick and it gets along fine.
You could also run an 8 inch out of one of the 70's mid sized Fords like a Grenada or a Monarch. I'd look for one out of a Leaf spring car so I didn't have to cut all the brackets off a coil spring rear end. Although Years ago I had a 61 Chev passenger rear end in the 48, it took about 3 hours of cutting and grinding to get the brackets off an get it presentable.
