Nic,
When I went the 9mm route, it wasn't hard. Here is a guide.
1st: Call Krista and Robert at
www.rbprecision.com2nd: Order 9mm Upper 1/2, a lower parts kit, and a 9mm hammer from them.
3rd: Order a VM-Hytech 9mm mag block from Brownells
4th: Assemble the lower parts kit onto your stripped lower
5th: Insert mag block and attach upper
6th: Insert unmodified UZI mag.
7th: Blow shit up.