66 273 Cam and Intake Thoughts

273 1966 heads have the "normal" bolt pattern,
double check the casting numbers, under the cylinder head {valve} covers.

I suggest either a stock type 273 4 bbl intake,
or an old LD4B, for use on a 273 or low compression 318.
I have a rare "Marine" 273 4 bbl intake, there are a few around.
The Marine ones you can use a 600 Edelbrock on without an adapter.

The smaller runner size will work better than the 340 sized
runners on the newer intakes.

If you want you can convert to hydraulic cam,
what rear gears are you using/ plan to use?

I am using 2.25" dual exhaust.
My engine is stock bore, low compression 318.(1973 donor)