Matt,
Oh, yes at 1/4 scale it's a whole different deal! My Vega cowl is about 13" dia. at the front and about 12" wide at the rear.
Without consulting the drawings, I'm guessing it's the same cowl used on the Altair...or if not, at least it would be very close in dia.
I'm guessing that the 70cc Minarelli is going to be enough power....I certainly hope so!

Nigel