Hello! Yes changed my username to match my race name. Royal ( Marines ) causes confusion in the Army team haha. As said yes I have a fuel tank from an 899. It's been rubbed down silver and has stomp grip, no dents other than the slight scratch marks you can see in the pictures on the corner after the Ducati sticker. I bought it as a spare for my old 1199S but never used it. There's a damaged one on ebay at £369 so happy to take whatever makes it worth your while. I paid £350 for it.
I think they are the same other than the 1199 is lighter aluminium whereas the 899 is steel? I'm on the way into work so can't check now but one of the guys did give me details of some differences with the stock subframe fittings on the 1299 / 959. Apologies if thats actually 899/959, but either way I dont think it applies to you since you have the rear aftermarket subframe?
Just found my post on Trackday Addicts facebook page. The 899/1199 are definitely compatible and it's just the subframe difference that shouldn't be an issue for you.
Yes, the rear mount is different. Nelson should be able to fit it to the race subframe, but he would need the pin for the tank and the clamp that holds the pin.