Thank you Brent and others for the info on plenums.

On my 235/320 I am in the process of building a plenum using the top cowl as
a mold.
Yesterday I pulled the fabricated piece from the cowl mold and using
clearance spacers between the new plenum top and cowl (for engine vibration
clearance) temporarily glued the upper plenum back into the upper cowl. I
carefully trimmed the rough plenum until I could get the upper cowl to fit
back on the airplane without any conflicts or distortions. I then attached
paint sticks to various places on the engine with 5 min epoxy extending up
and carefully glued them to the new plenum top allowing me to carefully pop
the cowl top off of the plenum and like magic leaving the new plenum top
placed exactly where it needs to go on the engine. At that point I used my
small drum sander to trim and rough up the areas where I would complete the
upper plenum and form it to the cylinders and various attach points with
release tape on the engine.

I am using a newly rebuilt engine that has no spark plugs in the cylinders
yet.

Last night I realized that there is probably not room for the upper plugs on
# 2 and 4 cylinders due to the close proximity of the upper cowl.

For the 235/320 guys out there using the original cowl, I am wondering if
you encountered this and what you did to resolve this problem.

Has anyone heard of a shorter plug that could work?

Any ideas greatly appreciated.

Randy L. Snarr
235/320