[b-man]

Not easy but definitely doable would be to find a way to get a TH350 or TH400 in that '57.

I would ask Goatracer1 about the specific details of his TH400 swap, however keeping your original 347 would require an adapter plate to mate the later trans to the engine and provide a place to mount the starter motor. If your car has bellhousing side mounts your adapter plate would need to incorporate these as well, look in the Danchuck catalog for the '55-'57 Chevy for a bellhousing side mount adapter to use or copy.

Getting rid of that expensive to rebuild and inherently unreliable original trans would make owning this car for the rest of your days a lot more pleasurable and would likely cost less than rebuilding it.