An impact can put less strain(depending on strenght of course) than a big breaker bar in some cases, while being more effective at breaking things loose because of the "impact" effect.

That being said, like George mentions, I wouldn't tear it down either...

You say that the coolant was a fresh green? That's a pretty good sign... Usually it's a nasty rust color if it's been sitting too long and not changed.

My take is that you should just start her up and run her for a bit and then change the oil and filter. If the car was under a closed hood, and something plugging the holes(even a rag), it's probably almost good enough to go. Hopefully. Taking a light and looking in the spark plug holes might tell you what's going on in there with regards to surface rust on the cylinders as a starting point.
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Kyle - 142, 145, and 244! - Oregon Volvo Tuners?