273 exhaust manifold interchange?

Not exactly. I had early 340 logs on my '65 and they fit. I also had power steering and when I took them out once, I noticed a small grind mark where they might hang on the PS box in unmolested form. Manual steering is OK. They do exit at different angles so youll have to adapt your head pipe to mate up, the 340 faces down, while the 273 faces back on the driver side. Magnums fit pass side, but the column hits on the driver side. They flow very well though.