Small block heads stamped HP??

[91r/t]

Just picked up a 72 360 longblock all rebuilt for 400 bucks....hell of a score! Guy said has newer model heads on it......get it home and look and they have no casting numbers on the runners where they all usually do. These are just stamped HP in big letters where the casting numbers would usually be. Anyone seen these before? The heads are open chamber heads and look pretty common but what are they? Any help would be cool! Thanks!

 

[91r/t]

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[91r/t]

 

[RustyRatRod]

The casting number is on the underside of the heads on the intake side.

 

[91r/t]

Ahhh thats wierd. All the heads I have seen had them raised up on runner humps on top side....hmmmm from all I am seeing online, these are 318 HP interceptor heads.....so they still flow like crap compared to modern heads.