Just buy the voltage regulator-brush combo and drop it in. Ie. with the setup you presently have, the brushes are in the alt. and wired to the regulator on the fender. The combo comes with the solid-state regulator attached to the brushes.

There's a pic at http://www.brickboard.com/RWD/index.htm?id=906600&show_all=1
which shows the regulator-brush combo. (Round black thing where your brushes go).
--
1980 245 Canadian B21A with SU carb and M46 trans

Mine had already been changed. Just get an alternator for an '84 240 and it'll bolt right up. My voltage regulator was still plugged in, but I don't know if you'll need to change any wiring to make it work. Good luck!

I'd just get the alt rebuilt. They are simple robust systems.
Usually brushes go, but your local rebuilder will be able to put
it on a scope and tell you.
It would be quite a bit more expensive to get an internally
regulated alt put on as you will be replacing an entire alternator.
Is the vr a problem? It too can be replaced if the alt scopes out
okay. My 81 still had its original vr on the sidewall; a PO had
a 55 ampere Bosch with internal vr installed... I wouldn't mind
going back to using the original, but a brush service cured my
problems (for $20 :).
--
Stef - 81 245 B21A M46 319000km "fat chrome" roofrack