Never saw this before!

Not related to 273 ci. clearance theory. Just a heads up I recently dropped a 360 ci. in my 64 and had a issue with the stock early A drivers side exhaust manifold. The 360 had the desirable 308 casting heads but with the air injection port feature below each exhaust port. I had to grind away some of the added material from the casting due to interference with the exhaust manifold. Only the rear port on drivers side. I found this out after I dropped the engine in and was a hassle to grind it in the car. Yes I drilled and tapped the smog holes then installed set screws to plug them. Went from 318 to 360 and was well worth it!
PS I have manual steering so can't comment on any power steering issue.