That's the one Mike - 1987 on...
I wish I could help you Simon but I do not know the differences, if any, do exist. There was the Ohlins suspension, steering damper bung etc. The big difference was the race kit Yamaha offered with the different exhaust, cams, pistons, oil pump and cooler etc. i used to work on one for a fella in the mid 90's but it was eventually stolen. Neat bike.....I wouldn't mind adding one to the collection.
Spoke to Peter Day on Wednesday - the UK expert on OWO1s and he has 24 of them so probably knows a thing or two LOL!
He gave me a huge list of things to check out so I'm hoping to go see it a week from today. I've wanted one ever since my first visit to the TT in 1993. There I was on the course for the first time doing 80mph around the verandah on my 125bhp ZZR1100 and next thing I heard this howl. To my right was a bloke on an OWO1 going round the outside of me like I was stood still, cranked over, knee slider sparking, staring at me as he passed. Ever since, I had to have one....maybe next week