I opened up my Airbox kit and began fitting it.  They give you pretty much a blank carb plate and I cut the hole

for the carb drain.  Nothing but DIY guessing here...

You have to cut the filter base to clear the upper section of the intake scoop so I measured how far forward this was from the forward

edge of the fuselage. 

Mine was exatly 24 1/2"

I the drew a center line on the filter base and installed it using small clamps to hold it centered on the Carb base plate.  I then installed the

lower cowling and lined up the filter base with the center of the scoop hole at the very front.  Then I carefully removed the lower cowling

and clamped a pointer to the crank to locate the center of the scoop opening. 

Since the filter base is actually on an angle compared to centerline of fuselage, using this pointer it will allow me to align the filter base

to centerline once it is trimmed back to clear the cowling above the scoop.

I then measured forward 24 1/2" from the firewall not the forward edge. (Note: This will give me about 9/16" clearance between the cowling

and the filter base)      

Not shown but I then cut the filter base at the line marked.  Then I moved the forward edge to the left to line my center line up with the pointer.

Worked like a charm.