I did the T45 my self and to me the hard part was getting the parts. But I kept at it because of the reviews saying how good the T45 is with the right parts and how much torque it can hold. I have pushed 400HP and 450T through mine, I am pushing 300/300 through it now. I did not go for the 28 spline input shaft because you really got to dump on the trans to brake the 10 spline but for a power adder then... I do not drag race but I do beat on the car HARD and with the Torsen diff that really limits tire spin I am pushing the trans to lots of torque multiplication. The stories of how smooth the built T45 made me do mine and it is smooth shifting under power and people that drive it ask me first thing what is the trans because they shift better than anything else. Is it true? I do not have enough experience to say but this set up is the best part of the car and makes you want to beat on it more. I am running a Steeda TriAx and that has been good and adjustable for 23 years.
As far as the build it self, it was ok, not easy but it is just bit fiddely . I have done other manual trans because when I got pros to do it I am disappointed with the out comes, I do it myself. The main tool is a GOOD big snap ring plier. A press to get the bearings on and off, if you do the bearings. I could not find much info on how to do the procedure so make notes and take lots of pictures. The problem I had was the sequence of assembly. I had to learn the pattern and that took time to take things back apart when I got too far ahead on one shaft and not the other. You can assemble a shaft but it is more of building both at the same time from the middle outward, If that make since, I would get too far ahead and have to back up, so it is do one part then go to the other shaft and add a part and jump back and forth.
It took be 2 days to get it right but I did it 3 times. Why because it was good BUT.. I would see or feel something and figure out what it was and what could make it better by adding a shim washer and that what was the secret, just getting all the slop out of it. I have some pictures somewhere. Over all I would be sad to sell the car with this trans in it. This is a Ford design problem from the bosses.. make it cheaper. Just changing a few parts make a world beater that would have made the T45 In high demand still but stock you can not give them away.
Sorry for the rant but it is not BullShit if you have done it.