I have just checked my old original chain, its 72 links.Chain is marked as 219TS. I sent my old chain to Andy the Chainman and he matched it up with a DID 219HTM racing go-kart chain and joined it up for me.
The timing marks are set at O, 18 & 26 links.
Be careful of buying internal engine chains from ebay, I bought a cam chain for the same bike and I could see it was the wrong one as soon as I took it out of the box! Same with the carb rebuild kit bought from M&P. Also the magnetic sump plug bought from M&P, it was the wrong pitch and would have stripped the sump thread!