Today I go the fins fitted and glued down with 30 min epoxy and milled glass fibre.

Next I fitted the spars, sanded off 1/16" per end and put radii on the corners.
Glue them in with 30 min epoxy. The are held in place against the fuse formers with a servo screw in the center and wedges in the slots that the spars fit through. The last picture has a red circle showing the screw I added to hold the spar up tight to the former. The screw was installed prior to assemble in the test-fit process.

A 2" True-Turn spinner was installed matches the cowl diameter dead on.