302 heads on a 65 273

You didn't say if your 273 is a standard 2 bbl, or a Commando 4 bbl. In any event, 302 heads are a great swap, a little clearance grinding needs to be done on the drivers side head, around the air injection holes, which must be plugged( tap the holes 1/4-20 and run set screws in, make sure they are below surface) for the exhaust manifold to lay flat.

With the 302's on, almost any manifold of your dreams is possible. If you like the stealth look, a Holley Street Dominator painted Chrysler Red works real well, Edelbrock Performer is also a good one, lots of inexpressive used ones out there.

Lots of small hydraulic cams out there, years ago I put a Crane Power Max 260 into a 273 that I had put a set of 302's on, worked out very well.

Good luck!