My mixture is set according to pilot jet size. I have a 50 pilot which factory pro provided and yes they are Keihin sizes. My mixture is set at approx 1.5 turns out. If you have 48 pilots you will find the mixture to be approx 2.5 turns. But these are approximate and you will need to fine tune maybe 1/16th to 1/4 maybe 1/2 turn in either direction according to other settings. There is no set setting.
Give the K&N a go, try the bigger mains, maybe shim the needles 1or two washers, then set your 48 pilots at 2.5turns and go from there. See how that feels.
Keep notes of everything you do and how it affects things so you can always revert back if needs be. And as Lloydie keeps reminding me, change one thing at a time, try it, then alter as accordingly. Once you start changing too many things at once it gets hard to know what affect one thing is having on another.
You could even become a carb addict like me.
(:-})