383 Build - Help!

Quote: I did not see an HP on the heads but I could have completely missed it.
Just by looking at the exhaust valves, is it possible to tell?
It does not appear to have any room for a larger valve.

The 915's you have may have been cast originally with the 1.60" exhaust valve and somewhere down the road someone had 1.74 exhaust valves installed which is normal. Those heads you got have the 1.74 valves and you can tell because there is very little (almost none) head material between the exhaust and intake seats and valves.

The 452 heads you mentioned are open chambered, essentially if you use them you will effectively get a larger volume combustion chamber which will decrease your compression ratio therefore go with the 915"s.