For the model year 1982, the B21A, B23E, B21F Turbo and Diesel had alternators with an output of 55 amps. The B21F CI, LH Jetronic fuel system and B28F had alternators with an output of 70 amps.
The alternator for the diesel had a special terminal labeled W that provided the pulse for a tach.

Son's 81 had a 55Amp. I replaced that with a 70Amp from an 84 which fit right in. The output terminal on the 70Amp was in a slightly different spot on the case, and we had to work the harness to take out all the slack to get the large Red charging wire to connect OK.

I don't think there would be many occasions when you would use the entire capacity of the bigger alternator, but the extra amps at lower RPM's is nice if you have big stereo, auxiliary lights, heavy use of rear window demister, blower, etc.
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Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)

Look up alternators at fcpgroton.com
Look under 240-engine-electrical
You'll find them listed for different years and what the amps ratings are.

The later years 240s had a bigger alt; I'd guess you could put one on an earlier 240 without mounting problems. But look closely when at the PnP. Or even test-mount one right there on another older junker.

On the fcpgroton site you can also look under 700 + 900 series cars and see what there was. Not sure if they interchange. But I'm pretty sure the 900's had a higher-output alternator than even the later 240s.

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DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).