Motorola Voltage Regulator

Doe anyone know what the Motorola voltage regulator part number is for the regulator model used on a 68 AMX 390, standard trans, go package, no A/C

Thanks Joe

R2AM1 or the R2AM2 which superceded it.

Poor choice of words on my part, pretty much implying they came factory that way.
There were a whole lot of them on the road, but not necessarily factory - dealer installed.
The R2AM1 has a much higher voltage setting, and a different thermal curve. I've seen a bulletin somewhere but wasn't able to find it again. I found the bulletin related to the alternator number changes, but not the regulator yet.
Many of the R2AM1 regulators got changed out due to over-charging issues. I did see a bunch of them on the road in the early 70s. My own 68 had an R2AM2. I bought it from the original owner, low miles. It may have been a dealer thing as he said he'd never had it in a shop to be worked on other than dealer/warranty stuff.

Interesting notes (to me, anyway!) the Motorola factory document and bulletins, cross-references and so on show a gap in the regulator listing - they show the R2AM1 as being sold to AMC through 1967 model year only.
Motorola shows they then sold the R2AM4 to AMC for late 1968, and 69 forward through 1970.
If Motorola sold R2AM1 regulators to AMC only through 1967 then what did early 1968 cars get?
Very late 1968 model year Motorola shows the R2AM4.
Can't say I've seem that on a 68, but then I've not seen the last few cars that rolled off their lines for the 68 model year either. I've not seen every single AMC ever produced........... only a few hundred of them, often the single-owner cars that came through our shop.
In any case, since none of us has seen all AMC cars for any given production year, there's bound to be some mis-match of documentation on AMC's part. And I've found more than a couple such mistakes in AMC documents.

While it's hard to imagine that you've not seen 'original' cars with the R2AM2, as I have seen a whole slew of R2AM2 equipped cars - they were actually more common than the others when I worked the old Rambler shop and many of the cars I worked on were still 1 owner cars, but they were a retro-fit. The AMC books were in certain years marked "use part number xxxxxxxx" which refers to the R2AM2 regulator. The R2AM1 number was still there, but the books indicated the other was the replacement. Motorola maintained the same exact stock number - the R2AM1 was a 5-24. The R2AM2 was also a 5-24.
It's hard to go by the AMC parts books and TSMs as they are very often wrong on electrical. They didn't keep up with reality. I've found even the wiring diagrams were incorrect! And I've found contradictory diagrams in the same TSM - one page says one thing, while further back, it's different. It's pretty easy to tell when you compare the documentation of their suppliers with what AMC says, they often fell behind or didn't keep up with the running changes or supplier changes.
I've also found that AMC at times referred to different regulators using the same AMC part number.
At one point they list a regulator for "Fleet/optional" and it turns out it was the same exact regulator that was used for all production the following year. I've found they didn't always wire the systems the way Motorola spec'd things either.
In short, I've found there are times one needs to do what's correct, not what AMC shows in the book.

In any case, for 1968, go by the pictures in the link the rev sent - as it's not the engine or equipment as far as the regulators are concerned. The engine and equipment DO determine the alternator, but not regulator. The regulator will be determined by the year and/or connector as some documents imply a change that may have taken place inside a model year.
If it's the bullet connectors, I very much recommend the R2AM2 over the R2AM1 as the 1 could over-charge your battery, depending on the battery technology/type. There's nearly a half volt difference, and higher isn't really a good thing if it over-charges. And 15.2 is pretty high.......
If you are in an extreme cold area, and drive a lot in colder weather, the R2AM1 would do better as the temperature curve is more suited for colder climates.
But go by the connector type.
Since AMC sold both the R2AM1 and R2AM2 for use on the cars of that year (if bullet connector type), and the parts book shows "use part number xxxxxx" which is their number for the Motorola 5-24, which is R2AM1 for a while, then it crosses to R2AM2 later, both would be correct.