PST 1.03 TORSION BARS

My bars were similar to Blu's. I had to pull them back some, and still had room.
Have you tried putting it in backwards? or even test fitting the other one?
My opinion is that those front sockets are very deep, more than deep enough, to accommodate 3mm.
I imagine grinding 3 mm off will take a really really long time,lol
If I had your problem and could not find the solution, I would drill a hole in the rear socket and insert a cotter pin in there, or a roll-pin, or a nail,lol. I have worked on several Mopes with missing clips; I wonder how important those clips really are. Even my own car lost a clip somewhere in time, before I caught it. I have no idea how many thousands of miles I might have driven without it.