I have read before that the U-joint shout be upgraded when doing gears? is this true? also on mustangtuning.com they also say you should buy a master bearing kit? my 96gt has 43,000 miles, would i need this or should i get it to be safe or what?
U Joints, no, unless you have problems with them now. Heck, if it were me and I had to replace U joints, I'd get an aluminum drivshaft as well.
With 43K on the clock, the bearing kit is a good idea.
As for your situation, I say contact Randy Stinchcomb over at www.modulardepot.com in their forums boards. They have a section entitled "Ford parts" and you can reach him there. He will be out of the office though in a few days so you might want to contact him as soon as you can. I got my 4.30's and main bearing and seal kit from him shipped for right at 230 dollars. I have had no problems either with my setup either. Car runs like a dream. Randy is a good guy to talk to and he is definately experienced enough to help you in this department. Good luck.
Id be leary of those plastic speedo correction gears. I took my white 4.10 speedo correction gear out when i installed my speedcal, and the thing was all chewed up. Missing teeth off it etc. I stuck the red stock one back in there and have had zero problems.