Standard transverse spring, Posie monoleaf.

Standard Poly bushings.

The bushings do fit into the perches, but they are very tight.

The bushings do slide onto the shackles when not installed in the perch.

I can just barely get the shackle to start into the bushing, maybe 1/4" at the most.

It almost seems that by "forcing" the bushing into the perch, the inside diameter of the bushing is being reduced, making it too small for the shackle to fit through.