I think going from a manual PTO clutch to an electric PTO clutch would be easy. Keyway slot in the hub,a switch, and safety wiring. Going the other way would be far more difficult because of the missing linkage.
You'd have to get it to fit the shaft and then worry about belt sheave diamaters.. Way too much trouble for what it's worth. Something like this: http://cgi.ebay.com/ebaymotors/A-C-Clutch-7-2-groove-For-York-Tecumseh-Compressors_W0QQitemZ290330669071QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item43990e700f&_trksid=p4506.c0.m245&_trkparms=65%3A12|39%3A1|72%3A1171I would like to hear more about the " modified automotive A/C clutch" ....