What folding mechanism and what buffer tube are you using?

MPA folding (same as hk dude dude but without the screw issues) and SB short brace tube

Are the frame/actions the same. Looks like the "57" has a longer butt?

There are different lowers. KH Dude is the small one (only in 9mm), mine is the full size and can be converted to different calibers... Or something like that

This is exactly what I want to do with the MPA 30SST or maybe even the MPA 10SST.  Don't own glocks is the reason I m not planning on going with your model but it looks like it is set up nice.  As a child of the 80s I have always wanted a mac style weapon but have always understood their uselessness in the civilian versions.  The ability to use braces and red dots is a game changer and has placed one of these as an imminent project.