Summit has adapters for 700r4 chevy pattern to bop. I am assuming a 1957 pont block has the same pattern as later buick , olds , pontiacs http://m.summitracing.com/search/de...-bolt-pattern/pontiac/transmission-type/700r4
I realize this may be a little late but ive got a hydramatic I would get rid of for the right price....
I have a 1960 Oldsmobile Jetaway that might help you out. You would have to exchange the rear bell housing from your old Stratoflight auto, but then the Jetaway would then bolt up. Let me know if interested.