Thanks for the lead. I didn't initially post there as I had pretty well sifted through everything I could locate on the web search and dead-ended. I came here basically looking for some knowledge about types of steels, annealing, etc.
It is a pretty straight forward piece and with the correct thickness of the proper material, it shouldn't be too hard of a project. Even laser cutting or EDM may be viable. After all AMT (apparently) did not do a particularly stellar job of manufacturing the part.
The Automag III in .30 carbine is a great piece, but there were a couple things that engineers could have been done better.