Gary,
The General Forums section has a current thread: "hydraulic top-link?" that has some good infomation. One of the posts has a link to a cylinder source that looks like a good prospect.
My tractor is a couple of versions out of date, but I just bought an auxillary outlet kit (Deere) that is available with either 2 quick connects (for one cylinder, ie top) or 4 quick connects (for two cylinders, ie top n tilt). You can use power- beyond for fluid and buy the 2 spool valve of your choice.
There are many old threads addressing this topic. Too many to confortably read on the computer screen (for me, at least), so I printed them all, read them at my leisure, and hi-lighted parts of particular interest. I also jotted down web sites mentioned in the threads on a single piece of paper for my own reference once I get serious about top n tilt for my tractor.
I haven't heard of anybody disappointed in their TnT. A question I have, however, deals with drift and settling of the implement once positioned using TnT. My loader drifts down noticeably in a few minutes. I expect the box blade or whatever is towed behind the tractor will drift and settle, too. I don't know if that is much of a problem or not.
I think I recall someone here on TBN saying that for precision work where drift and settling would be a problem, he repalces the TnT with the OEM top and side links.
OkieG