The snorkel does not sit perfectly square on the FM-150 since the servo sits out further than the stock Bendix style servo. This is how "I" modified my snorkel to fit, there may be an easier / better way but since I was asked how mine was installed here goes and a level of comfort doing simple fiberglass layups helps: When you bolt the snorkel to the FM-150 it will cause the snorkel to be approximately 7/16 too far forward when you get to the air filter assembly and the snorkel will not slide inside per plans. To start I made an initial trim to length of the snorkel. (this pic shows the snorkel square and was taken before I tightened the snorkel to the FM-150)
Next is to slit the corners of the snorkel so that you have 4 sides that you can move easily. These slits shown are preliminary, the final ones were several inches long - follow the contour of the snorkel.
Trim the tabs on the filter frame approximately in half, they are angled and won't allow the snorkel to fit with the adjusted snorkel sides. There is still plenty of flange to secure the snorkel
With the snorkel bolted to the FM-150 you can now screw the filter flange to the baffle and then push and hold each side of the snorkel against the filter flange and drill/cleco just like in the plans. Remove everything and epoxy the individual sides to the filter frame. Your snorkel now should fit without any tension but look like a mess because you have long cuts in each side. Scuff the outside only and apply epoxy and fiberglass over each cut then apply larger pieces to cover the entire upper snorkel. Several layers of 7.5oz cloth should do it. Don't add any cloth inside the snorkel.
Fill each slit gap from the inside with epoxy and flox and sand to maintain a smooth inside contour. (this pic shows inside prior to filling the slits with epoxy/flox)
Bolt all back on and you are finished.
yes, I know the plastic comes off of the filter before use
The final snorkel has the same intake area below the filter and nearly the same airflow pattern so I can't imagine there is any measurable difference in airflow from the filter to the fuel servo.