Tom,

I did that conversion on my restored '36 Chevy PU and I agree with Tim, Craig and Showkey. Mine was way more work than a simple gear change and is described in this article posted by a VCCA member:

https://vccachat.org/ubbthreads.php/topics/334876/1936-chevy-3-55-rear-gear-conversion.html

My '36 is way more pleasant to drive with the 3.55 rear gears and I would enthusiastically recommend it to anyone. It has the 1932-36 version of the synchronized Chevy & Pontiac 3-speed transmission, a crude device compared to the '37 and up units. The 4-speed of that era is an unsynchronized beast of a trans with a first gear ratio that, as Carl points out, is well suited to pulling stumps and probably also for moving 747s around at the airport. They are cheap, however. In fact guys have told me they can't even give them away.

Ray