I have the BAT 90 mm (3 1/2") MAF Adapter and the K&N RU-1785 filter (5" wide 8 1/2" long).
If I had to do it over again, I would have gotten the RU-1785 and the bullet Pro-M 75mm MAF. No adaptor needed, save the $45, and spend it on the Pro-M, instead.