Probably be the easiest if I can find one or just fab up a new guard, the trigger guard is part of the internal mag so ill need a new one. Im probably going to just build a whole piece that uses the original bolts on the receiver and weld in a lip for the front if the psl mag to rock in on and a paddle for the mag release on the back. Haven't decided if I want to open up the receiver for the mags feed lips or just leave it alone and modify the top of the mags. Those rimmed cartridges are real finicky about feeding so I'd prefer to just use the mag if I can afford to take more meat outta the receiver.
10-4. You may want to give the lahti 20 round mags a look. I know there were some guys modifying them to work in PSLs. I've never held one but they look like they might be easier to work with for a project like yours.