Cylinder head identification

[Sachmo]

I'm having a tough time figuring out this engine. My truck originally came with a 292 i6, or so i've figured from the vin. It now has a 350 from 1975 with casting number 3970010. the number on the front of the block is vo722txl from this i got that it is a 185hp van or bus motor. The cylinder head has casting number 3998991 which tells me the valve size but not chamber volume. It also has gm 73 cast right above cylinders 3 and 5. I'm wanting to see what the compression ratio is and whether these heads are any good. Thanks in advance fellas!

 

[Sachmo]

I forgot to mention there is an upside down t shape underneath the long string of head numbers

 

[crazy4offroad]

3998991 307, 350, 75cc, 72-73, 73 had hard seats

 

[Jims86]

3998991 307, 350, 75cc, 72-73, 73 had hard seats

Exactly what I was thinking...Can you see an marksmon the front of the heads, maybe get us a pic?
Most of those heads were the same smog headsnup to 86, which arenthe same heads that GMPP is using on the 290/350. they havenkinda a lopsided trianglemcast on the front of the heads for Identification.

 

[Sachmo]

The front of the head has this shape. The shape is also cast under the valve cover.