Back in "the old days"
of Controlline flying, the profile fuselages were made out of balsa ranging from 1/4" - 1/2" thick (depending on the engine used ). Then a 1/8" lite ply doubler was glued to each side of the front of the fuselage. The doubler extended back to about 1" - 1 1/2" past the leading edge of the wing. Inside the doublers were maple blocks to fasten the engine to.
To do it yourself I suggest the following:
1. Mark the width and length of the engine on the balsa part of the fuselage. Now from the width of the engine mark the location of the maple engine mounting blocks. Do not use basswood for this as it is not strong enough. You also want to mark the wing location on the fuselage at this time.
2. Now make the cut out for the engine width only on the balsa and also cut out the wing location.
3. Lay the fuselage on top of the 1/8" lite ply and trace the outline of the front part of the fuselage including the leading edge of the wing opening and the engine width opening. Cut these openings
4. finish cutting the opening in the fuselage for the engine blocks.
5. Glue on ONE piece of the lite ply to the fuselage and when dry EPOXY in place the maple engine mounting blocks. Glue the other lite ply doubler on and clamp/weight down until dry.
Your landing gear is either going to be mounted in the wing or it is going to be through bolted through both pieces of the lite ply doubler and fuselage.
Your wing will slide into the fuselage opening and be epoxied in place making a NON REMOVEABLE WING. Depending on the accuracy of your cutting of the wing opening and the width of the balsa fuselage, you may also want to add some filets at the wing/fuselage junction for additional strength. We didn't use the filets "in the old days".