I'm getting my '68 ready to drive again after 7-8 years of sitting. I hear a low-level growl noise in the rear on a short test run.

1. My u-joints are 145,000+ miles and 56 years old so I'm replacing them.

2. Over the years I've had rear axle bearings fail on both sides a couple times. I even have a bit of paranoia after one failure decades ago had one cut about 1/2 way through the axle. So, I'll be checking and likely replacing them too as preventative maintenance.

3. Now, where I need advice: I understand the noise could also be an axle pinion issue. Researching, I find no source for new 2.56 BOP ring and pinion sets.
If that's the problem, is used the only route to find them. I'm hoping, if new doesn't exist, other owners upgrading their axle ratios may have some good used 2.56 parts available. And, if the noise is differential related, are the other parts generally available?