Here is a quick pic of the car prior to air ride. When I bought it, the previous owner had cut springs on it.
I like it! looks sinister and low, and I dig the steelies and dog bowl / copo type caps.
I concur with Dave. I would recommend a th400 or a 4l80e for a big block, but you *can* get away with using a th350, 4l60 or 700r4 for easy cruising. Some of it depends on your rear end and desired gearing as each of these vary with 3 or 4 speeds. Each of these transmissions also vary on their overdrive percentages. a 4l60 has a decent low first gear with decent torque, for example.
it really depends on the intended use. It also depends if you want pure hydraulics or if you want electronic control. I would go with a th400.
Free Trivia: most tv shows from the 70s and 80s with show cars that would come standard with a th350 were always switched to th400s because of the amount of abuse the transmissions could endure by the stuntmen performing 360s, reverse driving, jumps, etc.