I'm lookiong to get a RRA 9mm upper with their mag block.
Since I don't have "colt" I'm not going try "colt" mags. Mainly because of the price.
Does anyone have the specs to modifiy uzi mags?

Or is this a bad idea?

No its not a bad idea if done correctly:...The problem is I cant "tell" you how to do it...I mean I cant say "Cut a 1/4" slot 1.25" from the top"..Etc..etc.The reason is that every rifle or maybe every Mag block and the position of the mag block might be a little different...Just a little....But enough to make the mag not work..Anyway heres what I did and it worked fine....Buy 1 preconverted Uzi mag,Best place to buy from is Rockriver themselves,But only buy 1!...Set your rifle up to run with that 1 mag....When you get the rifle running with no bugs buy a bunch more unconverted Uzi mags and use the cut one as a pattern.Just about any good machine shop should do them for less than 10 buck a piece.......UNDERDOG