Why so much RPM? There's no need. Look at NHRA cars, they're turning 8k on the limiter at most (not talking top fuel, here).. Nascar engines are turning 9k but are built bullet proof to get there. The reason they do it isn't because they want to, it's because they're displacement limited and need more RPM to get more power. Power is a function of flow. Flow is a function of displacement and rpm. If you get capped on displacement, the only place you can go to is RPM. The VTX is not short on displacement!
If you de-stroke, it's not a compression issue. If you de-stroke and use stock pistons it is, but why do that? Custom taller pistons will make up the compression, but now you're slinging more weight - you've just negated the entire reason to destroke. If you want a light piston, you want a short piston, which means a longer rod. If you're going to spend the money on a custom crank, then you've got the budget for custom billet rods too. Rods are steel though, so they increase their weight significantly more than the piston does as you make it longer... see where I'm going? Not to mention that adding bore to get some displacement back...
You want to start with a short throw engine to begin with if you really want to minimize stroke and maximize RPM. The 1800 is not that engine. Heck, you'd be hitting close to 100 mph with the stock gearing in second gear!
Now, going back to reality, what do you want the engine to do? You can build something streetable that's brutal or build something completely bonkers that's race-only. Revving high sounds awesome, but isn't needed for big power. Maximize port flow, punch out the valves, ramp up the compression, go for moderate duration, maximize valve lift and get some decent valve springs into it, massive intake with plenty of runner volume to feed the heads and direct it all through a 'microsquirt' fuel injection setup and you can realize some great potential. All of this can happen at less than 7k rpm, and the engine can live at those revs if your rotating assembly is properly balanced. It'll probably even do it on stock rods and pistons.
The engines on these really are stout. The decompression lobe is a weak spot, but guys have run these bikes with turbos, super chargers, big bore kits, and though things DO break (always do when racing) it's always at ludicrous power levels and there's rarely any one part that gives up consistently.