4l80 behind G3

You will need a adapter bellhousing anyway, all of the swap headers are designed around a driver side starter. That is also one of the reasons you dont see the NAG-1 trans used is A-B-E body swaps, passenger side starter. The NAG-1 can be built into a robust unit like the 4l80 but nobody makes a swap bellhousing. SRT8 manifolds work with some mods I hear.