oh... er...
well, after sitting in the workshop for a few minutes with a craft knife i finally thought "to hell with it" and cut the throat bit off the front of the air box, the K&N filter popped on a treat.
i took it for a spin up the road and performance was sh*te to say the least, then i remembered i left the choke on, after that it was great. the bike now has a deeper, growling exhaust note and the power is instant when you come on the throttle. all in all i'm quite happy with it. will do a plug chop to check the mixture is still okay but i think it is fine (bike was up-jetted a few sizes when the exhaust was put on and ever since it has been a bit rich and absolutely stinks the carpark out when idling) i think its been a success
will possibly get a pic or two tomorrow