Well I ended up selling the Mastiff before I got around to fitting the tank, so I have for sale a decent condition KTM LC4 tank (with twin fuel taps). iirc it's about 18 litres capacity.
Hopefully an example here:

Now they seem to be selling for stupid money, (http://www.ebay.co.uk/itm/KTM-640-Adven ... 337f5b398a ), but if someone on here was to offer me £100ono they could walk away with mine....
Oh and I'm in central Scotand so if you want to collect from me, easy, if you want it posted I'll have to check the cost.
Cheers,
Smudge
smudgegs@yahoo "dot" co "dot" uk
Oh yeah pics: