Mike -
Having the same range of motion on your hydraulic toplink as was on your manual one helps, but how important it is depends on what implements you are using.
If you are looking for one for your TC 25D, I had one installed by my dealer on my TC 33D that should work on yours. They had two options: one was just about as long fully extended as my original was fully retracted. It also had only about a 6" range of motion. That was obviously not going to work (even if I welded an extension on, I didn't like the short stroke on it). I opted for the longer one, which would not go quite as short as my original, but extended out further. It has an 8" stroke. I tried it as-is, and found it worked OK for some implements, but could not shorten enough to tilt my box blade forward to a good angle. Fortunately, there was a bracket on the fixed end of the cylinder that I was able to get cut down as short as it would go... this is working out well. I may eventually cut an inch off the shaft end, but have not really needed to up to this point.
If you are considering a hydraulic top link for your 25D, let me know and I'll try to get the brand and part number off the link for you.
John_Mc