67 Dart 273 swap to 383
With those b bodies manifolds it is a TIGHT fit. I ran them when I broke in the 383 in my dart (it’s an original big block car). They hit the firewall.
Everything you said can be done to swap in a big block. You didn’t mention if your car was column shifted or had a console. There is more massaging to get the column linkages to work.
I know in my car (big block k frame and reproduction big block motor mounts) I needed to use the federal (or a trw) power steering pump due to where the connections are located. But I am also running a stock power steering system in my 67