Compression test??

They are on 360's in the late 80's to early 90's. They have a great exhaust port and pretty good intake port. The valves are 1.88 and 1.60. Those are small enough for your 273 but probably bigger then what you have. The chambers are around 70cc and you could get smaller with some milling.

These number are with stock valves and valve job....

Stock ported(home ported)
int. exh. int. exh.
.100 58.0 42.9 62.2 48.0
.200 123.3 78.4 121.3 79.2
.300 171.6 110.9 183.4 114.1
.400 193.8 129.9 218.9 142.6
.500 208.6 136.6 227.8 155.7
.600 214.5 139.8 228.1 158.9

Superflow 600 bench @28inches