[Treeve]

Don't believe the hype of a T56 - go a TKO600 instead, the gear ratios are effectively the same 1-4, and it's not like you really will notice 100-200rpm cruising difference. The gear shift is infinitely nicer 2-3 on a TKO than a T56, and the gear shift location can be exactly where it should be for a cobra with a TKO.
For engine, it depends which state you're in but it's not impossible to get a Windsor rego'd, and that's the way I'd be going over a Coyote or an LS.
Don't do an 8 stack as you won't pass emissions or noise testing.