Update:
I've acquired a couple more torched midsections, and bought a couple front stubs from Czechpoint. My plan is to use the donor sections as filler for the cut areas, hopefully being able to use the existing rail profiles in the donor sections to match up with the original receiver.
The donor sections were cut at right angles to the pieces I have, but some careful measuring and a little headscratching tells me that I can basically flip the donor pieces 180? lengthwise and the rail profiles will match. (If you look carefully at the pic above you'll see the piece in front is backwards.) The Czechpoint stubs were cut long, so I should be able to reconstruct the magwell from those sections fairly easily.
I'm building an alignment jig out of 1/2" plate to keep everything straight and square during the reweld process:
I'll cross-drill the FCG holes and use pins to lock it all down.
Question: Anybody want to help out a ban-state brother with a magazine shell, or a 10/30 conversion? It's legal in CA to have either a magazine body with no other parts, or a 10/30. But I need something for getting the magwell sized correctly... Czechpoint is out of 10-round mags with no resupply on the horizon.