Questions on T56 Mag. before I pull the trigger.

[80Camaro]

I like the "turn-key" T56 Magnum kit from American powertrain. I spoke to Bill who was very cool. I will be replacing the TH350 in my '71 Camaro. Their kit includes their Stg 1 Street Slayer clutch which I am not familiar with. Also, Bill assures me that the OE LS style bell housing will fit my '86 and up 1 pc seal 350 block... that I would only have to shim the slave/throwout and not use the top center bolt hole. I was under the impression the LS hsg would not work with an old school block. Opinions? If I am missing another company to check with who offers everything I need for this swap, let me know!
BTW... my engine now is at approx. 420 hp and just a little more torque but an LS is in the future with 550 minimum.
Do you guys like the close or wide ratio version? I have 3.73's with 26" tires. Thanks all!