I have determined that the alternator is bad on my 1980 240 with the external voltage regulator.I have a 1983 parts car, but I think that it has an internal regulator(haven't actually gone to my brothers storage lot to verify yet.) Are they interchangeable? If the '83 has the internal regulator,can it be made to work, or will I have to get an alternator off of a 1980 ext. regulator?

Yes, a very good upgrade. You may remove the old external regulator from the car and add it to your museum. Even if you needed only a new set of brushes, it would be cheaper to upgrade to the internal regulator, which has brushes attached and simply fits into the same location as the brushes alone used to occupy.

By the way, if anyone can find replacement brushes for the internal regulator, kindly let me know.

Or you can try online one of the worldpac vendors like this one no questions asked.
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Art Benstein near Baltimore

Cfinn, the local starter/alternator rebuilder should sell you brushes. The local place has always sold to me, $2 ea. There are different dimensions of brushes, for diff. Mfgr's. I just looked at the two pairs that I have left and one is .180" x .250 the other set measure .190" x .310" so pull your brush holder and take it with you. (they both have copper wire pigtails attached) Be ready for them to tell you, that "you can't do that"... tell them whatever you have to... tell them that you are a shop teacher, yeah that's the ticket. Tom

Yes - the '83 alternator will work. A decade ago, when I replaced the alternator on my '81 DL, the dealer sold me a replacement w/internal regulator and said it was standard practice to upgrade older cars w/external regulator this way. When you install the newer alternator, simply bypass the external regulator wiring.