The F2 is pretty universal, many of the other sizes are functions of the choke size, of each other, or both.
You could go larger than 36, but unless the head is done well it won't do much.
A stylish air cleaner will throw the whole thing overboard - even some of the most expensive are worthless. You need a large filter area (square inches), but also the cover is way too close to the air-horn in many of them, should be at least 3" away for my taste (the usual rule is twice the air-horn ID; 45mm × 2 = 3.54"). Too close not only restricts air entry, but also causes a signal reflection off the cover that confuses the venturi and emulsion tube.
