After speaking with Bryan at Showplanes, I realized that I needed to install several small gussets on the intake plenum mounting flanges.
Fabricate gusset plates from remaining f/g sheet used for plenum mount flanges.
Roughen all bonding surfaces.
Tape gussets in place using packing tape.
I also decided to reinforce the lower lip of the intake plenum.
Mix epoxy and wet out 2 pieces of 1" f/g tape.
Apply tape to lower lip of plenums.
Mix remaining epoxy with flox/cabo.
Apply epoxy mix to inside corners of gusset plates.
Next, I worked on fitting the oil door to the cowl. This piece was included with the cowling and is molded for the correct shape. The door was slowly trimmed to fit the recess in the top cowling using permagrit tools. The recess edges were also squared up. It took some time but the door fits nicely in the recess.