The 55 - 57 trannys were cantilevered and they were cast iron. I have a 55 hardtop that has run a muncie since the early seventies with no issues. This car has seen a variety of small blocks and big blocks which pushed it anywhere from mid 14's to mid 12's. I broke spider gears, side gears, ring gears, and pinions in the stock rear ends and never had a tranny issue. Upgraded to a dana 60 and haven't broken anything since. The driveline in this car has been abused severely. I would not worry about the lack of a tailshaft crossmember.
John
