273 2bbl turn into Commando or is 318 better?

What year is the 273 64-66 have closed chamber heads but 64-65 have a different intake bolt angle. Build the 318 if the 273 is the right year use the heads, crank and rockers.
268 solid cam, 9.5:1 compression, 1.88-1.60 valves ported heads, headers, Eddy rpm intake and 650 Holley 350+HP.