I know that either the part number or the cast number end in 561 but which is it. I have a set of heads that mayyyy possibly be 561's.... Can someone give me both cast and part number.... Thanks....

 

99% sure the GM p/n is: 12551561 [someone else possibly can verify?]
it's the GM p/n that ends with 561 not the casting #
I don't know the casting #for the 561's

 

On either head, cast into the outside/top of the intake runner the casting # will end in 561. Also, on the outside just below the two center exhaust ports, there's a "D-9" cast into them.

 

thanks again. You have me on a mission now. I know that they cannot be ported as much as regular heads, but if I do have the 561's they are fully ported and polished. I picked them up a few minutes ago with old head in one hand and the new one in the other and as long as I am not crazy, they new ones are pretty significantly lighter. Might just be SOTP feeling type thing, who knows....

 

I remember weighing a newer 561 vs. a 94-95 casting & they were a little bit lighter IIRC, but I honestly dont recall the #'s. They do feel a lil lighter though when carrying them around & even moreso when they've been pushed as far as they'll go