That's a setup that is optional for that engine. Far and away, the most common setup is a 1 inch keyed shaft and 4 bolt mounting. I suppose you could pay a premium, custom order it from somewhere, and hope you get the right engine when it comes in months later. Keep in mind that BCS has put adapters and cone clutches on their new machines for 20 years now. Why wouldn't they just order the engines to these specs instead? You also gotta make sure it's a SHORT tapered shaft. The long tapered shaft is for generator applications.
Another note. You're looking at a 7 hp engine. While it'll be nearly as powerful as the 10 hp gasoline engine you're removing, you should consider getting a 10 hp KD 420 instead.