Thanks again Dan for the excellent guidance. I already built the airbox with airway dimensions equal to a 3" dia cowl opening. I should mention here for others i addressed the aluminum plate cracking and glass bottom chafing by using through bolts to the servo with tubes on the bolts inside the filter to control compression. Of course bolt heads are saftied.
I thought the new glass to rehab the cowl cutout was not handsome. The irony is an elbow with the servo horizontal requires the same width cowling bubble to clear fuel fittings and linkage.
So, the box is ample size for a 2 1/2" inlet you suggest. My only unknown at this point is how much to clearance the cowl "rehab" for shake clearance ? I have roughed in 1" pink foam but some guys have suggested 1/2" to 3/4" is OK. The only really cool looking option would be a rear facing horizontal servo on an elbow with a belly scoop, but the air box/ filter would be demanding