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.

--
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).