here is how i rationalized it when i was going through my tranny debate(i got the T56).
first off the torque rating is around 500lb-ft. above what a stock block is gonna handle.
secondly i was swayed with the slightly lower 6th gear, and the 5th gear that can be used for racing--i like to go fast.
the way i look at it is if you have a dart block combo in mind and MUST have a manual then the tko 600 or viper spec T56 is in your future, if you have a stock block then the T56 will take damn near anything you throw at it.
as for the install it would be helpful to know if you have subframe connectors. if you do then you will have to cut the brackets that you get and weld them to the body.
if you don't then you can bolt them to the frame. either way you will most likely have to cut the rear crossmember attachment to make room for the supplied tranny crossmember brackets.
i am installing full length subs on wednesday and have to do the cut and weld, i will have pics the following tuesday night of how i did it--its not that hard.
other little things that have to be done are enlarging the spacer plate hole for the clutch cable, and rerouting the wiring harness(no modification was needed). i was unable to use a 3 piece mac x-pipe, but since put a summit h-pipe on it that fit good. wednesday i am gonna try a
bbk x-pipe to see if that fits(i like my x-pipes).
all in all it is pricey and is somewhat of a trial to install, but to me the benefit is worth it. i will never consider another tranny for my car--ever.