[blucar]

Some people like the big & little look, I have never liked that look. I like the same size tires front and rear so they can be rotated to improve tread wear. On a car I think P235/75R15 is to large, that is unless you want the "Rod Look" in lieu of a traditional factory look.
The recommended wheel size for a P235/75R15 is 6-8.5, where-as a P205/75R15 is 5.5-7.5.. The diameter of the 235 tire is 28..91", which is very close to the average 600x16.. The diameter of the 205 tire is 27.11". All of the tire sizes are per Coker's catalog.
From my point of view the Columbia with 3.78 ratio would work well with the P205 tires. One thing you should keep in mind when considering over-size tires is the brakes on your car. The braking power of the '47 brakes are marginal at their best in today's traffic, adding over-size tires (P235), could "INCREASE" the stopping distance. Think of the tires as being large flywheels rotating down the road.
Lots to think about when you start messing with "Henry's original design.