Today I went to the site and checked it out, and it looked a lot better than my overly active imagination had made it out to be.
Thankfully, there seemed to be zero actual moisture under the tarps; it was bone dry under there. Here are some photos of what I found:
Right after removing the first two layers of tarps. I took off that shrink wrap that was left over from shipping since it could make moisture cling to the engine (if it got in there).
This is the only visible casualty of the moisture so far. I think a bunch of moisture collected around the shrink plastic that was wrapped around this crankshaft end a while back and did the damage.
I cleaned it up with a metal finishing pad and a bunch of rags, then coated it with grease.
The rest of the engine looked pretty unchanged by the passage of time. The aluminum didn't look much worse than it did when I transported the engine to the site. I suspect that most of the moisture damage happened when the engine was still in the back of my work truck, since a puddle formed in the bed nearby it.
You can sort of see how the aluminum has "spots" on it now.
Relatively "high and dry."
I pulled the shrink wrap off. You can see the rural yard there.
I noticed a little rust forming in the groove in the crankshaft where the V belt goes, so I cleaned it out with WD-40 and a rag.
What are these rods that I can see in the exhaust ports; are those valve stems? They didn't look rusty, but they did look kind of dry. Or at least half of them did. I gave each exhaust port a quick shot of WD-40 in there to keep those rods oily.
Now here's some of the stuff I stacked on top of the engine before putting the tarps back. I found it at a local hardware store.
Then I placed one other type of anti-moisture deal on top of the engine. Hopefully it won't dry it out so much that it cracks all those nice new hoses!
Back when the engine had just been delivered, I called Steve at Proformanceunlimited and asked him about storage. I told him that I planned to store it outside with a tarp over it until I was ready for it, and I asked if that would be OK. He said it definitely would, that I shouldn't have any problems with that at all.
Then today I got to thinking about that, and I wonder if they put anything special in the cylinders and turned it over before shipping the engine, like some really thick grease/oil or something to help preserve it. Naturally lots of the engines they ship won't be installed for a while (a year or more, perhaps), so maybe they plan in advance for that. I'll call on Monday and ask.
If they didn't do anything special, I'll take the good advice and put a little oil in each cylinder before turning it over.
When I'm facing the water pump, I should turn the crankshaft clockwise right? Also, would anything bad happen to this engine if I accidentally turned it over the wrong way?
Thanks very much for the excellent advice!
-Robroy
I would check it just to make sure no water gets in. I have a couple 390's and a couple of Y- blocks stashed in an old school bus. I shot oil into the cylinders and screwed the plugs back in. I can still turn them by hand and they've been in there about 20 years. 
