Correct Voltage Regulator

[1959retractable]

I am seeing multiple amperage readings for voltage regulators for my 59 Skyliner. Which is the correct voltage regulator for this application? It has A/C and power windows/seats. I see 30 amp, 35, amp, 40 amp, etc. Is there a "correct" one?

[Ford Only]

Most of the early Fords used the 30 amp generator, I know they had a heavy duty 40 amp and the case was about a inch longer than the 30 amp.
Without testing there is no way to tell for sure unless the amp rating is stamped somewhere on the generator.
I think that if you used the 30 amp regulator it would work just fine it just wouldn't allow your generator to charge at more than 30 amps even if it was rated at 40 amps.