A rear PTO for these tractors are very hard to find but the are out there. Mission Manufacturing MAY have new ones but I'm not sure on that. Basically, these are nothing more than a shaft that mounts on pillow blocks under the length of the tractor and is driven off the front PTO. I believe they have a female connection on the back and turn counter clockwise or opposite almost every other PTO in the world. When I get a chance, I'll have to see if I have any info on this. I've owned Power King tractors for almost 20 years and I've never seen one of these. They do come up on ebay every once in a great while.
A universal three point could work with some possible alterations. That's just a guess as I've never tried it but, hey, it would seem to me that a three point is a three point. The big thing is to make sure your tractor is set up for a three point. Not all of them were. If you have a piece of bar stock protruding straight down from each rear axle with a hole through the bottom to accept a bolt, then you are good to go. Sorry, that's the best description I could give without a picture.