Factory 911, 914/6, 916 air boxes, How many different designs? Options

[horizontally-opposed]

Went to the dyno to do a first dial-in on the carbs and made 169.9 hp at the rear wheels with no air filters. Was pretty jazzed, and then the dyno operator said "Now watch when we put the air box back on...it'll be even nicer."

We lost 20 hp.

It was the end of the day, and I still need to finalize exhaust before we really dial the thing in, but we pulled the snorkel and air filter to do one more run. We gained 12 hp back, so 162 hp at the wheels. This from a 2.2 six with E pistons, a bit of compression, Solex cams, a bit of head work, headers, a single-tip Leistritz muffler (now a two-tip Dansk sport muffler), and Webers.

My question: How many variations of the factory air box were there between 1965 and 1973? Carbs, MFI, T, E, S, etc? I know there were metal ones and plastic ones (my air box is plastic), but I'm wondering if anyone knows a link that explains the variations, or can provide Cliff Notes from which to start my research? I'd love to keep a factory air box on the car, as I like the noise reduction, but would like to get some of that power back. Engine also feels hesitant past 6000 rpm.

I know, I know—rain hats. I'd prefer not to go that way. Thoughts?