Dave,

You might also consider some engine fogging. It is made for laying up engines. It is available at marine shops, and may be available from NAPA. I've only used it on a non-running aircraft engine, so I fogged it by cranking it with the starter. But, you can read the directions on the can and see if you are supposed to do it while running or while just cranking it. It's kind of like Uncle's suggestion with the oil down the cylinders (which I have often done also) but because it is being "breathed" through the engine it might get in places that would otherwise be missed.

I can't remember if someone else already suggested it, but if the cars have nice tires on them, you might want to get the weight off of them with some jack stands.

Charley