As much as I hate to add fuel to this fire......
I am contemplating going a different route to increase displacement. Stroke. We use a local company to do crank regrinds at my work. I've talked to the guy that owns the place, and he said taking some material off of the rod journals is cheap as can be. I've run it through a few test in Solidworks and if I got the variables close, it 'should' hold up under normal use, but I can't be sure until I try. Making the rod journals a smaller diameter greatly increases the stress on the crank, and add to that the extra stress of the higher displacement. In my experience with doing this in 2 strokes, things tend to only last half as long as they do stock.
Benifits of this? If I take 1 cm off of the rod journal diameter, I can get about 480 cc out of this motor. I still have to take a look at the motor, but I dont think that at this stroke any modifying will need to be done to the crankcase. Standard pistons can be used.
The downsides? Increased stress as already mentioned. Custom rods and bearings need to be manufactured (still slightly cheaper than custom pistons and sleeves). Compression ratio needs to be kept in check, so either a thicker headgasket will have to be made, head chambers dug out a bit, piston dome material removed, or a combination of these. Or use race gas.
Bottom line is, this ends up being less work than going big bore, and slightly cheaper than having bigger sleeves and custom pistons made up. But at the same time, the motor will not last long. Not a big issue if it isn't driven 5k miles a year or raced each weekend.
Whenever I get a quote back from Crower on the rods, I'll post it here. Will probably be around $500 a pair.