160mph? Interesting challenge, don't think I would want any more high up weight than avoidable, so once a cage is on then you probably want the fuel to be as low as possible, over the rear wheel might be just about the worst place possible! Just how far do you need to go on one fill? The standard tanks are at least fairly low down.
The rear tyre and gearing issues could be sorted out by finding a larger wheel and lower profile Z-rated tyre combination with a slightly larger rolling radius and find and fit a slightly smaller sprocket. There are motor sport oriented alloy wheel manufacturers who stock rims as blanks that are then machined to suit the final application; they should be able to copy the centre of the M3W wheel and it can then be bolted to the standard hub. You'll probably have to extend the swingarm a bit to get correct belt tension but you'll probably need to stiffen the swing arm and improve the clamping of the spindle to take the load anyway so the extension will be a minor detail really!
18" rims on the front should give a selection of bike tyres that will take the speed but I have no idea if the spoked wheels will stand the loading at that kind of speed.
I have a feeling that getting the (theoretical) power for 160 is probably the easy bit - depending on how long you want the motor to last at max revs - and the rolling chassis will be the awkward bit to sort out. Definitely don't want to get to 159 only to find that a wheel isn't up to the job.
Best of luck!
