Scooterotica

Hi, I'm interested in buying a new engine case and with standard ones costing almost £400 I'm am consider one of the new type with the bigger gasket face, like the GT or Casa. I know they will take a standard 200/ 225 cylinder but what cylinders are on the market or in the pipeline that are able to be bolted on using an "outboard" bolt pattern so giving larger transfer port areas? By that I mean not studs going up through the barrel and head.
All this is for future upgrades but I'd hate to buy one that isn't upgradeable.
All information will be gratefully received. Thanks Dave