727 transmission are pretty easy to rebuild once you gain a little bit of experience and buy a handful of tools. The first one I did took me a week since I slowly studied each part as it came out and figured out how to put it back in. By the time I rebuilt my third one I could do it in a day. Race transmissions which are typically nice and clean both inside and out can be rebuilt in a couple of hours if you have the parts on hand and know what you are doing.

One thing you have to really watch out for is the part changes over time. You can get really screwed up if you mix and match parts from different years. You have to either stick with one transmission at a time, or else you have to pay a lot of attention to the various splines, seal positions, oiling passages, etc. If you accidently mix up the parts the trans either won't work or will eat itself.