To clarify Tally's statement - PCB mount stabilizers need to be installed before the plate is installed - otherwise it will not fit.
Assuming you've soldered everything, you *might* be able to get away with using screw-in stabilizers without desoldering (probably not though, just throwing an option out there). I do not believe the plate is made to fit plate mount stabilizers.
If screw-in stabilizers don't work, I don't know what to tell you besides desoldering everything to install the stabilizers on the PCB.