Well, you weren't thinking of it in this way, but the pulley diameter can make a difference on alternators. The replacement internal regulators for GM alternators require 1000 rpms to kick in. Once the regulator turns on the rpms can be reduced and the alternator will continue to charge. I learned this when I put a 10SI on a Ford 8N tractor. You started the tractor, pulled the throttle 3/4 open, the ammeter jumped to charge, and then the throttle could be cut back. The initial guess was there was something wacky about the regulator but this was a NAPA regulator and the parts catalog had the disclaimer about the 1000 rpm. On a modern car, you may or may not even encounter this problem since 1000 rpm is slightly more than a fast idle. But on a tractor that tops out at about 1800 rpm and the pulley diameter ratio is around 1.5:1, you notice it. A small flathead like a 134 would probably be much the same.
Well, I was using the pulley from the 8N generator and I didn't have the option of a smaller pulley. You can see though, that a smaller pulley on the alternator would cause the regulator to kick in at a lower engine rpm.
Now one solution would be to find a factory original internal regulator, but there is the problem with identification and if that unit went bad, then you are back to the original problem.