You could do the degrease soak without any damage. Follow that with a scalding hot water bath and some dish washing liquid and a scrub brush. Scrub the snot out of the thing - it's cast iron for heaven's sake - and then hit it again with hot water. If you have a pressure washer and can hook it up to your water heater that will work pretty well.

A few pointers - wear goggles and be prepared to get really filthy yourself. This will also make a huge mess where you're working. A fairly good and inexpensive method to contain a lot of the mess is to by a cheap hard plastic (not the inflatable kind!) kiddie pool and set the engine in there to work on it.

After all the degreasing and washing, put it on an engine stand (if you don't have one - buy one for $39 at Harbor Freight) and dry the entire assembly with compressed air (keep the eye protection on) and then go everything with a soft dry cloth. Go over the exterior parts you intend to paint with lacquer thinner or acetone (wear gloves) and then use a good engine enamel.

Let it dry really well and then spray light oil over all the exposed parts and rotate the crank assembly multiple times, making sure you get oil around all the bearings and the cylinders coated. DO NOT USE WD-40. TRUST ME HERE! Then cover the entire assembly (on the stand) with a big heavy garbage bag and tape it shut. Store it inside, preferable in the garage - not outside in a shed.

That should do it - may have a bit of surface rust if the oil doesn't cover, but you should be okay to store it this way indefinitely.