I would never just use wood as a support for a pivot pin or spring. I would make a base frame of aluminum or steel and cover it with the wood grip. If you just use wood (even laminate) as the base support, it will eventually wear through or break out.
The smg in those pictures still has the FCG in the standard location. You just need a trigger bar to extend back and clear the magwell.
Any high capacity pistol magazine would work for a copy of this. High-cap Glock or S&W magazines come to mind.
For 9mm, .45, etc. blowback, you would still need to modify the bolt/carrier similar to what I did for my conversion. If you really wanted to make something interesting, use Desert Eagle mags and make it gas operated in .44 or .357 and keep the rotating bolt system.