Bad things often happen if you convert a 1000 PTO implement to 540- they're 1000 because they require more torque to run them at 540 than the PTO shaft can handle. And most tractors with enough snort to handle the 1000 PTO implements will at least have 1000 optional.
I think I'd go with the other suggestions and just round bale it. I was a loan office at PCA when the stack system came out- not a very good system, apparently, because after a couple of years they were gone. I think they were the most useful for big ranches with remote fields- you could fence off the stack and self-feed out of one side- very handy in big snow country, where you have trouble getting feed to the cattle in a blizzard.