i had a gm rubber clamshell motor mount, a 5" long 7/16" bolt fit through. THe engine bracket can fit up to a 9/16" bolt. The bracket on the motor and the clamshell and the 5" bolts are stock. I put in the new polyurethane inserts into the clamshell. the 7/16" factory bolt wobbles around in there alot. i tried a 1/2" and 9/16" bolt and they dont really make it all the way through the poly inserts. the outer part of the poly inserts are 9/16" but the middle is smaller. advise?