in the gregorys manual i have it shows the pointy cap for the box type air filter housing, this manual does not cover the twin mower so i would assume that style cap was fitted to several mowers.
i know i had one on an old housing i had laying around, not sure if i still have it. i have to tidy up this weekend for my daughters 5th birthday party next weekend. if i come across it ill put it aside for you otherwise ill sort the shed out the weekend after her party [3 weeks from now], if it turns up ill work out a way of getting it to you, but dont hold your breath im not sure if i still have it
by the way is the fuel gauge cap still in one piece ive got one but its smashed really should throw it out but it makes a good spare.