Fixed it... swapped the spark plugs around (and cleaned them up a little, they had some gas on them), then used a stronger battery jumper than the portable one we used whenever it seemed the battery was draining. Turned it over, it ran rough at first, then started right up.

It burns oil like a mofo when its run at higher RPMs, but it runs... God knows whoever ran the engine before dogged the hell out of it. Poor D16. I'm keeping extra coolant and oil on hand in case it burns oil a lot or leaks coolant from some surprise location.