Tom, and All - I got an AL74x in pretty good shape from a 114 junker sedan some years ago when I was just getting into the alternator upgrade issue. I had read here that some Bosch 55 amp alternators used the same plug as our 113s and others required alterations to the wiring harness. Models AL74 and AL72 were mentioned in that context but in reading all those posts I never learned which was which. The donor 114 used a different plug than my 35 amp alternator and, unlike my car, had no external regulator on the fender near the intake manifold. Plus, there was no evidence that there had ever been one mounted there, particularly as the alternator wiring just joined up with the rest of the sedan's wiring harness, leading me to the conclusion that the change in wiring at the alternator connection and apparent elimination of the external regulator in the wiring system meant that the AL74x in that car had an internal regulator. Multiple vendors were offering the AL74 as being of the internal regulator type, which seemed to confirm that conclusion. I chucked it and kept looking because I wanted to stay with the original wiring design, including connecting hardware, in my car. Couldn't find such a creature in the boneyards, so eventually bought and installed my AL72x as described in previous post. And that all seemed to make sense at the time -- plus has served me and the Pagoda as our maker of electricity very well ever since.
But now I'm puzzled. I've seen AL74x models for sale described as both having, and not having, internal regulators. And, sure enough, the only one I can find around here does indeed not have one inside. And if I remember my setup correctly, I'm pretty sure its connector socket wouldn't mate up to the wiring on my 113. So, does this represent a period of transition? [I'm thinking they might be easily converted with a slick re-design of the brush carrier.] And I don't even know on what models the AL72 appeared in original production. [They seem to be less common than the 74s.]
I am now certain only that an AL72 fits an early 1969 280SL with no alterations necessary, full stop. [Also quite pleased that the vendor sees fit to supply it fully equipped with fan & pulley assembly and requires no (AL72 or any other) core in exchange.]
So I'm sorry, Tom and All, for misleading you, and hope there have been no bad outcomes or inconvenience as a result. The fittings for conversion of AL74s to our cars is a solid find, made valuable to many by posting it here, in line with the fairly fabulous results you're getting with threaded rod, Tom.
