I would choose between the 4sp OD gear set or T56 Magnum. The TKOs are not worth cutting the car up.

Silver Sport 6sp kit is nice but after you add bell, hyd setup and clutch to the base kit you are over $6k.
Passon gear set is $2K if you have a 4sp car.
So is a modern designed trans with 2 extra gears worth $4k more?