273 4bbl intake manifold question

First, verify what heads are on the engine now. Pull the valve covers and get a casting number.

64 - 65 had a unique intake bolt angle and smaller diameter bolts than the "standard" 66 and later engines...

The 64 - 65 heads are hard to get intakes for.

I would recommend replacing the heads with a set of 66 and later heads and have hardened seats installed on the exhaust valves. Then you can get any intake for the LA series engine...

The 273 - 318 has the "smaller port" heads where the 340 - 360 have larger port heads and bigger valves... However the combustion chambers on the 340 - 360 mheads are larger and will lower compression about one point if you put them on. Then the intake valve clearance to the block is tight. Not much room to put larger valves in the 273 unless you "notch" the bore for valve clearance, and then may get some shouding.

You need to provide more info for any cam, or intake and header recommendations. Like what do you plan to do with the car? Street, strip, cruiser, or race???