273 Piston Question

Removing 2 of those 4 eyebrows will drop 1.5 cc's from the equation... not a lot. The real compression drop vs the high CR is the lack of the dome, not the eyebrows.

And the 57 cc chamber is for NHRA minimum chamber spec 273 closed chambers..... production closed chambers are in the low 60's. So, no, in stock unmilled form, the 273 closed chambers are within 0-2 cc's of the 302's and Magnums.

The later open chamber 273 heads are around 68 cc's. The later ones still had decent CR in the high 8's with the 4 eyebrow 273 pistons and thin head gasket due to the much higher compression height versus the 318 (around .070" taller).