First let the engine run at idle until it is completely out of fuel [try re-starting it several times] Then put 5 or 6 drops of after run oil [or marvel mystery oil] down the carb and glow plug, re-install the plug and spin the engine over with your starter for 4 or 5 seconds with the throttle open. Remove the engine from the car.
You can then wash it off just be careful not to wash dirt into the front bearing [even if it has a rubber sealed type]. I brush it off behind the flywheel then rap a strip of cloth around the crank, "wedging" it between the front of the engine and back of the flywheel. I then plug the carb and exhaust [be sure there is a glow plug installed] then squirt it off with methanol or denatured alcohol [Not Isopropyl it is 30% water]
I do not recommend brake cleaner or motor spray.
Then blow of off with compressed air if you do not have compressed air shake the engine vigorously and blow it off till dry with a hair dryer, being careful not to get it HOT just warm to the touch. Last I remove the strip of cloth let the engine come to ambient temp [so there is no condensation formed inside] and put it in a zip lock bag!