Being as my old wans will prolly be buried under less crap than you old wans, I'll go have a look.
Okeedokee, all the Mikuni toobs have the prefix number 611.
1991-1995 Mk1 and XTZ are Y-4
1996-1998 Mk2 and TRX are Y-2
Are you aware of the Factory Pro toobs ? They nickel plate theirs and reckon they won't wear for many thousands of miles. Unfortunately, they're based in the USA and it costs a small fortune for us in the UK to buy them. Just thought I'd mention it as it might be an option for you to try this method.