Dookbob,
I did not know that point you made about the skirt being larger than the face, but I can see why now you've said it. Every day's a school day. Might make those measurements kinda hard...I'll see what comes up.
Utopia,
You are basically walking down my thought process.The bike has had a baby belly pan on it for a good while, but it doesn't do much in the way of blocking air flow to the header.
Kato,
The point about the forged vs casting makes a hell of a lot of sense. I was actually talking about buying a second hand rear piston (since they are dirt cheap) and sticking that in, but I do realise that if it is of the same era then it will get noisy again after a while.
At the end of the day, I don't exactly give the poor wee bike an easy life. I bought 18 months ago with 19k on it, now it has 37.
Again, thanks for everyone's input!