273 exhaust manifold ID help needed

Can't help on casting number, but if you are using the original frame and steering from the '50, get yourself a mini starter or a starter off of a Dakota. When I had the 318 in my 51 Plymouth, I started out with a stock starter and the end just touched the steering box, and had to slide the tranny back to change starters, I switched to a Mopar performance mini starter and it gave me a lot more room.