f4u:

The engine box is not glued in. You mount the engine on the firewall and then slide the engine box in or out to make the back of the prop 9" from the fiberglass fuselage cap, then glue the engine box into the fuselage. This is mentioned at the bottom of page 8.

Before you glue the engine box in place it would be a good idea to fit the cowl over the engine and make sure the prop clears the lower corner of the cowl by 1/4 to 1/2".

Jim