Along with all the other information, a lot depends on how it looks under the covers. Dried on crusty stuff should be scraped and scrubbed then rinsed down. Just dirty oil can be cleaned with a oil and diesel, kerosine, or ATF mixture. No driving with diluted oil. I am assuming there is no oil filter so change oil often till its clean enough for you. If you can afford to let it set ( days or weeks ) with a full block full of diesel or kerosine, that would be best, it would give it time so soften up some of the really stuck on crude. If you do let it set with a full load of cleaner, pull the spark plugs and rotate the engine every day a few turns with the starter to expose all the parts to the cleaner mixture.
Joe
