Your 4-speeds are all the same as what was available in your '54 and all have a direct final drive. No overdrive so no RPM reduction.
It sounds like the rear end choice really comes down to which is in better condition, or easier to install. Assuming you have stock gears now you will get a little RPM reduction from the change.
The T-5 does have an overdrive and would give you some RPM reduction, but most versions of it are real stout. You may be fine using it, but I'd be worried about using it and pulling a trailer. Even the stouter T-5's were never used in trucks or bigger cars.
Just how heavy is this trailer? Maybe its small enough not to matter, and maybe its big enough you're nuts to consider using the T-5.
