Good luck with the project - sounds interesting and will be keen to see the dyno charts.
With the valve and port sizes as they are it is going to struggle until it's at high rpm. The domed piston's not going to help either. Not sure it will be that much fun to ride on that big 690 platform.
It will need extensive head work, smaller valves, welded chamber, new exhaust. To make potential it would need cam development - as is you could reduce the lift quite a bit as you won't need the flow.
I think by the time you've got the head sorted out you may as well have left the bottom end alone, sleeved the block and focussed on the head.
Sounds like you have good people involved so I'm sure it's all been considered. If you haven't done so already i'd happily run it through some simulation if you can give me the port dimensions and flow details - must be readily available for the 690.
Are there enough potential customers to recoup your investment time and costs?