I found the number on the left head "20". Now what's the difference between a "20 and a "23"
62 Starfire 394

 

I think the #20 head was for a 1961 Starfire .
It had smaller valves than #23 which was used in all '62 thru '64 394's .
Post the number stamped in the center of head and I can tell you more

 

This 394 engine block casting number's ending in "4 1/8 with the number "20" on the heads which is a 1961 Starfire engine, low compression, so a 394 engine block casting number's ending in 4 1/8 with "23" heads is a 1962-1964 Starfire, high compression? Am I close

 

The 1961 Starfire had 10.25 to 1 compression and #20 heads .
All 62 thru 64's had #23 heads , whether they were high or low compression .
The piston dish depth , or lack of one , was what determined the compression ratio '
1962 and earlier engines had cast iron timing chain covers , 63 & 64 were aluminum .

 

Thanks Charlie