If you want OEM, then your only hope is used. And, as you've found out, not all used is good.
Topline makes new heads. I've heard nothing but positive reviews on their heads, but I don't know if the casting quality is the same. They can be found at PartsPlaceInc.com. Prothe (yeeeeetch) sells AMC. Apparently their castings are ok, but the valvetrain parts suck.
So, pick yer poison.
I'm happy to be wrong, but I am under the impression that ALL mechanical lifter heads are the same. The only difference of which I'm aware, is in the exhaust valves which are sodium-filled on TD heads. Like I said, I'm happy to be wrong. I KNOW they are different in the pre-chambers on later Hydro heads, but I don't know on the mechanical.
Th casting numbers are useless for identification. Of that, I'm certain. Many mech-lift head had the "T" or "F" suffix, but that's not a great identifier.
If I'm right, you can just try to get another mechanical head (TD or NA).