#1 on our list was to remove the alternator cover and see if we could turn the engine(this on advice of Trenton, Brian Sydness and Mike Stewart - Thanks guys!).
We removed the cover, put the socket on and started turning clockwise - no resistance, no 'noise'. So we turned counter clockwise and had some resistance and some 'noise'. In this case, noise means that we felt like the pistons were moving in their cylinders. As many of you know, one of our fears had been that over the years of slumber, rust would have formed between moving parts and prevent them from moving. It seems that that fear can be put to rest.
We replaced the alternator cover. We opened the oil filler cap and removed the drain plug and began draining the oil. Oil that drained out was cleaner that we had feared it might be. Once the flow had slowed down, we punctured the oil filter to drain oil from it, then we removed the filter and let the whole business drip while we took a break. We came back and installed a new filter, then replaced the drain plug and began filling it with synthetic oil.
We also had bought replacement air filter elements so we went ahead and installed them.
We had pulled the carbs last time and had later worried about the holes that were left open, so we took some clean rags and covered the four holes.
Now as to those carbs - we have started to open the carbs and clean the components in carb cleaner. I'd like to accurately describe what we've seen, but I'm not sure I'm (technically) up to it. Take the float bowls, they're mostly clean, but at the bottom there has been some residue. The main jet, jet needle holder and float needle has some amount of residue as well, however 30 minutes in carb cleaner and they appear to be as good as new.
Oh, remember the gas tank cap that wouldn't open: the locksmith who 'picked' lock was unable to make me a key, saying the cylinders were "damaged". He also said that the smell was getting to him, could I come pick it up as soon as possible! I stopped by at lunchtime and got it, and he wouldn't let me pay him for picking the lock - he said that getting that smelly gas cap out of his shop was all the payment he wanted!
And remember my comment that the tank was 'a rusty mess'. Let me amend that description by saying that rust may/may not be accurate. Could be chemical additives in the gasoline which have decomposed/settled. Significant flushing with water has brought some relief. And a kreem kit has arrived by mail order, so we'll let you know.