a pto winch itself is fairly simple, usually a big worm gear driving the cable drum with some sort of release mechanism to allow free spooling, they are available from very small all the way into the 50000lbs plus range, the drives can get very tranny / t-case specific, some trannys are not able to accept a pto but most granny low four speeds will have a pto port on them. winch ratings are kind of a gray area here, an electric 8000lb winch will rarly (in my experience) pull anywhere near 8000lbs, I base this on experience, a friend was stuck on a log and two 8000lb warn electrics wouldn't do the job but my 8000lb konig pto had no problems pulling him out, the limits are cable strength or ultimatly the strength of the worm gears. best bet if you have one is to travel with a buddy who has an electric, use the pto whenever possible but the electric should you have no engine.