First thing i would do,borrow another lower or two from a friend to try.This will help discern if your lowers have the mag catch located too low from spec.
Second,replace your mag catch.Cheap and easy to replace.If yours are worn down they will locate the Socom block lower in the magwell.
Third and this will require some welding.Take one of your old mag catches out and run a bead across the top.File the bead down to about .025 high,and then file about .025 from the bottom in order for the catch to fit into the receiver hole.With some smithing this should work.This will raise the Socom block higher in the magwell so a little may be have to taken from it's top also.
As Tweak suggested,measure your lowers with a dial caliper and we can compare measurements.
Don't give up yet.You can fix this!
FWIW, i built a dedicated 9mm using a new PWA lower,RRA lower parts kit,RRA standard A2 stock,RRA two stage trigger,Socom block with sten mags and a OLY 16 SS upper in 2002.Maybe i got lucky but it runs flawless.
Oh and another thing.
Happy New Year !!!