Speedmaster makes a cast iron Magnum stock replacement head.
Speedmaster makes an aluminum LA head that is basically a copy of the Edelbrock Performer RPM LA head.
EQ (Engine Quest) makes a cast iron Magnum stock replacement head.
Most likely EQ and Speedmaster are getting their cast iron heads from the same foundries.
Edelbrock makes a Performer RPM head with smaller chamber, Magnum intake bolt pattern, Magnum front accessory holes, but they use Chevy rocker arms.
Almost forgot, Trick Flow 190 heads take LA intakes, but the ends are supposedly drilled to also accept Magnum accessories. I still need to mock up one of these and see how it works out.