Hey, where is this going?
Sounded like a great idea, 10hp diesel in a bike.
I have some done some swaps in the past,
converted a diesel van to 4wd,
put a 50hp enduro motor in a 17hp quad, put a CVT snowmobile engine in a Honda XL250, V8s into Mazdas and Toyotas, and a bunch of other stuff over the years. I am a machinist and millwright in industry, maintaining and improving machinery. I know the work involved. This is a very do-able project.
Where are you now? You have the engine, do you have a bike frame?
I read about 750 and XS1100 chassis. Kind of heavy but ample room to work and good for a test bed. Not what I would use for the final bike, too heavy. I would be looking at smaller frames, but heck, get it done with what you have at hand! Nothing is perfect the first time around.
Transmission. You will need one. 10hp will not move on a single speed. Bike transmissions are wonderfully simple and very adaptable, especially from 2 strokes where you can saw the front half of the motor off if you wish. Motocross bikes like the YZ125 have too close a ratio transmission, enduros or quads are a better choice. It was mentioned in a post about the Yamaha Blaster transmission. I am very familiar with it. 6 gears with a wide spread and able to handle over 40hp without a problem.
Clutch, if you used a bike lower end you could also use the bike clutch and reduction ratios for the diesel engine. Remove the crankshaft and replace it with a through shaft, with a belt pulley on one end or the other. Epoxy is your friend. The entire Yamaha Blaster engine weighs 53 lbs, remove the crank and cylinder (cover with aluminum sheet) and you have less than 40 lbs. This is do-able.
Steve