I have a couple of Uni-Filters left here that come with a preset rev limiter of ~5,500 rpm
if I can find them you are welcome to them, they are rubbish
I use air con gauze on the standard airbox set up, same as Cam, which reminds me, Bevelman was supposed to be dropping off a roll
all my bikes are running Mikuni's so no airbox, am running DNA air filters