Wrong heads for a 273

My personal experience on bracket racing 273. Combustion chamber volume not measured in either case:

Stock 273 heads, (port matched to 340 intake gaskets), 10:5 to 1 factory Commando style pistons (forged TRW). Block decked (cleaned up cut), heads milled (cleaned up cut). Edelbrock Tarantula intake (made for 340) and Holley 600 CFM double pumper. Steel shim head gasket. Cyclone fenderwell headers and Isky camshaft. Best E.T. 12.72.

Same as above with 340 open chamber heads (2.02) and cylinders notched for valve clearance. Best E.T. low 13.00's.