Hi Danny, as far as I know, zev mags were not fitted to 101s generally, as most export models to Europe were fitted with Bosch Dvar magdynos. However, as a 42 degree mag it is highly likely to have come off an Indian, possibly Hedstrom, power plus or pre 1922 scout, or possibly fitted by someone as a replacement. It will fit, will work fine, and is an excellent magneto, particularly if you have a good one for only 500 bucks.
How is the rest of your bike ? Would you be interested in doing a short story on it for the next wow mag? Anything else we can help you with ?
cheers,
Tim