RE: cleaning old engine
Dismantle the engine completely. The bearings can be left in place if they are not rusty. Get a crockpot that will never again be used for cooking food, unless of course you want the ultimate high. Set it on medium heat. fill it with the cheap green anti freeze, not the red stuff. Submerge all of the engine parts, except rubber, in there. Leave overnight. The antifreeze will remove all of the burnt on grease etc. Rinse under a tap. Dry, oil and reassemble.
Depending on the case material the may be some discoloration.
Ed S