As far as a home grown conversion goes, a two stroke engine is a lot easier to make into a diesel. Business was a little slow over the winter at the motorcycle shop I worked at when I was in high school, so we used to pass the time by working on the shop race bikes and building crazy projects. One winter we took a used bike with a 125cc Sachs two stroke and coverted it to a diesel. We'd hook up the plug and turn on the ignition to start it, then remove the plugwire and turn the ignition off and ride off. Low side of decent horsepower, lots of torque - if it had a 6 speed transmission with overdrive 5th and 6th gears instead of a 4 speed, it would have been a bear, lol. Here's the shopping list of modifications to convert it to run on #2 fuel oil:
1. Weld up the combustion chamber in the aluminum head and regrind it to yield 18:1 compression ratio.
2. Weld 4 disks to the 2 crankshaft throws and weld straps around the disks so that they became round flywheels - this is one method of "stuffing" the
crankcase on a two stroke to increase the compression ratio in the crankcase to improve flow through the transfer ports.
3. Re-balance the crankshaft back to factory percentages.
4. Drain the fuel tank and fill from our heating oil supply (same lube oil ratio as with gasoline).
5. play with the jetting in the Bing carburetor until it ran right.
Sachs apparently built a really sturdy engine; we played with it and had a great time showing it off until mid spring, then took it apart again, opened the combustion chamber to about 12.5-13:1, didn't touch the modified crank and sold it along with several other used bikes. Spring a year later a young man showed up on my doorstep and told me he wasn't complaining, since he could beat all the other 125 cc bikes in town, but he wondered why it would only run properly on high test gas. I explained what was different about the insides of his, especially about how the crankcase was not just stuffed, but severly stuffed.....
