We are wanting to put a T5 tranny into a 1957 chevy Sedan and still use the bellhousing from the 57.  It was a 6 cylinder car that we swapped out for a 350.  we are not sure if or how this can be done and are looking for some pointers.  

I believe the input shaft on the T5 is longer than the factory 3-speed in the '57, so I don't think you'll be able to use the same bellhousing will work. To install the T-5, you'll need to install an aftermarket transmission crossmember, and also have a correct bellhousing.

Give the guys at Classic Chevy International a call, they can help you out with getting the parts you'll need for this swap.