After a long hiatus I decided to drop back and see whats going on over here. I don't have a v8 z anymore, I did about 7-8 years ago. My setup was a 72 with a mild 350 and a t56. Performance was pretty decent, very quick rolling 20-100 for sure (I mean like rolling to on the freeway in a few seconds phenomenal). My setup was less than optimized but I did get a good feel for what the car could do and having driven the car on two 1300 mile one way trips I can comment on the overdrives in the t56. Here's my gripes with the T56 and the Z car with the rear end ratio's they typically have (can't recall what they were, but think it was in the 3.90's or whatever). First gear gets to redline before you can blink. Second, Third and Fourth are your money gears, picks up lots of speed in those gears. Fifth would have been actually enough overdrive with rpm's under two thousand rpm's in fifth. Drop into 6th and your seeing 1500 rpm's and thats at like 70 if memory serves, may have been 65. Couple the redundant 6th gear overdrive with the hassle I personally had of converting a automatic 240z with clutch setup, tapping the plastic hydraulic clutch setup and it subsequently leaking a little (which I didn't even notice till I sold the car and we were checking vitals). If I were to do it again, it would have been automatic all the way for MY usage.
I think the thing to look at is what are your uses, how much highway time do you use it for, how much strip time if any, and your expectations, pays your money and takes your chances and hope your right. Hey if not, change it over, its just some parts and since they were modified for a V8 Z (like the driveshaft for example probably being a difference length between automatic and stick) you'd have a quick sale to a brother here that's trying to get his V8Z on. Good luck with your project I'm sure you'll enjoy it, if circumstances would have been different I would have never sold mine.
Regards,
Lone