Local Bronco friend bought his '76 brand new, and from almost-new it went through rear u-joints about every 5 to 8 thousand miles. Literally 40+ years and however many miles, and who-knows-how-many u-joints later, and he finally fixed it just a few months ago.
Found out that when he took it in for some warranty work on the rear end the first month of ownership and they replaced his whole housing, nobody ever noticed the misaligned pinion.
And in all those years he never noticed any unusual vibrations. Probably in part because he didn't know what to compare it to, but also in part because the vibrations must have been very small.
After correcting the pinion angle we're still waiting to see if they last longer. But even though the jury is still out, confidence is very high.
Even though there are plenty of other potential culprits in your case still, it doesn't cost anything to verify your pinion angle is correct. If you've seen enough of them, you can tell just by looking at it if it's going to be a problem or not.
Paul