I have a Mechtech upper. It takes the frame of either a Glock 19 or 23. You simply slide it on with the little ramp insert, which is in the little ziplock bag, and it becomes a 9mm carbine. I will also include a30 round magazines, it's not a glock but some other generic brand.
This is the version with the extendable stock. It retails for $499, I'll take $400 obo. only trade I'm interested in is ar part; especially high end triggers, barrels and/or matched upper/lower receiver set. http://www.mechtechsys.com/glock.php