I doubt if that is a double-stamp MAC. Original PS MACs usually have the barrel retaing pin on top, visible when assembled, RPB usually has them on the bottom of the barrel not visible when the gun is assembled.
I say USUALLY because if I use ALWAYS someone will prove me wrong.
A wise man never says never...

My double stamp comment was based on a couple of other items, but the photo may not show them well.
The take down pin looks "weird". Perhaps it's the photo, but it looks too slightly too large to be an original one piece pin. It's almost like it has a small button head, but I'm too lazy to dig mine out to compare. Along that same line, I'd think the take down pin release lever and clearance slot should be visible in the photo but perhaps the angle isn't right.
MDG; it's certainly no sin to not have all the answers. A double stamp gun will have the exact same roll mark on the right side of the lower receiver as your original photo, but there will be an additional roll mark on the opposite side of the gun's frame which reads;
RPB Industries Inc.
Atlanta, GA U.S.A.
If you don't already own a copy of Frank's excellent book,
The MAC Man, I'd highly recommend purchasing one. It's very short money for the definitive book of all things "MAC" and it contains a ton of great information and photographs. We owe him a huge debt of gratitude for his work in compiling this information and are very fortunate to have him, (and several other RKIs), here on this forum.