if it were me, I'd run the 465 and 300 unless you are going make a doubler with the 205 (203/205 doubler) then I would go that route.
the t176 was a medium duty trans with first gear around 3.7:1, it was found behind V6 and very underpowered V8's
the 465 is physically about the same size, it's a HD trans with a first gear around 6.7:1 (6.67:1 to be exact I think) was found behind some v6 but also behind any v8 gm produced and diesel motors.
depending on teh t-case you run, the 465 may or may not need adapters. the t176 will need an adapter regardless just to bolt up to the 400 (since you typed sbc, I assume it is really a 396 block from a truck)
the D300 is a good T case, takes modifications well, but they are pricey. decent low gear of about 2.6:1, does not take shock load well at all, cases are known for cracking.
the 205 is a beast, big heavy, thick castings.. but low gear is miserable, I think it is 1.8:1, not very good, but you can build a doubler with a NP 203 range box, you can also do a low-max gear swap as well as plenty of shaft spline count interchangability and upgrading.
