Hi,
usually I get my lip slots (for the wooden bodies) done with a jig saw before painting and final coating. In this stage, the slot is slightly larger than the bib, but after painting and coating, this problem is solved and the bib fits just perfect.
As I am using polystirene + thinner as a final coating and polycarbonate for the bib, I glue it into the pluc with one part special plastic glue, called Bison Plastic. I am from Romania, don't know if Bison is available on US market.
Kind Regards from Romania