If you like doing more with less like I do, keep the 273. My '65 Valiant four door went a best of 12.72 ET at 108 MPH with the small valve, stock cylinder heads (port matched to 340 intake/header gaskets).

Later,the same .060 motor was used with 340 cylinder heads (cylinder bores notched for intake valve clearance). With the 340 heads, the vehicle never broke out of the low 13 second bracket. All I could figure is I lost considerable compression after installing the open chamber, bigger valve, 340 cylinder heads.

With the 273, I used a 4.56 sure-grip (super stock springs), Mopar four-speed was launched and shifted at 6000 RPM and trap speed hit 6400 RPM. It did have a bad ass camshaft, the full competition Isky 312 degree (advertised) .580 lift monster. That did not keep me from cruising Main Street on the weekends (Salinas, California).