The voltage regulator only controls voltage. In fact, I've seen adjustable voltage regulators (internal type, for the later alternators) meant for cases where the car's system voltage must be kept slightly higher (year-round cold climate, different kind of battery, etc.).

But merely setting the voltage higher cannot deliver a reliably higher amperage, 55 to 70 amps. It might seem that way from a cursory view of ohm's law -- i.e., amps seems to simply be a function of the load's resistance and the voltage applied, so theoretically it would require going from 13.5 volts to just over 17 volts to raise the amperage you want -- but this impractical. First, simply raising the voltage will eventually (actually, very quickly) "cook" the battery -- wet cells are not able to survive when kept at higher voltages indefinitely (even though it's optimum voltage is temperature dependent). And second, the car's own electronic controls (ICU, ECU, ABS, SRS) will not prosper at such high voltages.

But the main problem is that the alternator physically cannot sustain, reliably, a delivery of current higher than it is designed. For more amperage at the recommended voltage, you need different diodes, coils wound in the alternator housing, etc. (together with better cooling capacity -- alternators generate heat proportional to their delivery of current -- those fan blades on the pulley are there for a reason*). A good rebuilding shop can rebuild your alternator to a higher delivery, but it isn't as simple as setting a different external voltage regulator or internal regulator/brush set combination.
[ * in fact, on a Mercedes I used to have as an illustration of the cooling problem, the alternator was equipped with an air duct that provided cooling air from behind a firewall behind the engine compartment.]

Replacing a bad external regulator is easiest. Substituting an internally regulated unit with the brush set (as suggested elsewhere) is a little bit more challenging, but not formidable, because of the rewiring required. But you nevertheless want to adhere to the recommended voltage levels for the sake of your car's many systems, not to mention the lifespan of your battery.

But if you really need a reliable 70 amps for your '79 240, then you have to upgrade your alternator. But what would you need in a 1979 car? Likely, the A/C compressor isn't being used (I'm guessing that your A/C system can't hold Freon anymore); you may, of course, have two or even four e-code headlights running 150W bulbs (and if so, for your car's wiring's sake, I hope you're using a relayed wiring harness for them), but the only OEM big amp user, otherwise, is your rear window defroster and maybe your fan if you run it on "3" all the time. So the only possibility left is if you have an aftermarket radio with a gigantic amplifier and speakers.

would that mean then I can just swap out the brushplate to one that is for an internal regulated alt?


Yes. That is exactly what it means. The newer regulator and brush pack are one unit.

Below are three views of the it (borrowed form FCP Euro).

Remove the brush pack for the external regulator from the alternator. Then remove the external regulator.

Install the new style regulator/brushpack.

That's it. You are done. No wiring to fool with really.










--
'80 DL 2 door, '89 DL Wagon