Zak- My gut-feeling is that the screamin' shroud sound was a pre-existing condition... that the previous owner went lookin' for it, using a pair of tin-snips rathern' lifting the motor out, and decided to give up.
If yours was bolted together like mine, there'll be four bolts with either 7/16" or 1/2" hex heads (don't remember)... two up by the cylinders (one probably holding the ignition coil), and two down at the bottom. pull it off, don't be surprised if all kinds'a junk falls out... and then look for metal that's been scraped shiny. Also look under the flange of the flywheel (between flywheel and block). You might find stuff wedged in there, and you may even hafta pop the flywheel off to get it out, but try to drag it out with a coathanger first.
Keith- I know you know what I meant... it was an old Engineering professor (the kind that really WAS an engineer before becoming a professor) that gig'd me for that once. Something about the significant-digit identifying an acceptable order-of-magnitude for round-off... where with 0.02, you could round 0.025 either up, or down, while with 0.020, you could only round up or down at 0.0205. I think that might've been the only explanation of notational math that was ever sensibly applied in my stay there- the rest was done by theorists, not practicioners. I figured it out well enough to pass, but they sure could've done a better job. :-}
IIRC, plug gap (which was one of the original subjects) should actually be more like 0.028". Whoever suggested replacing the Champion with something ELSE (like an AC-Delco, etc), I'll second that opinion- I've had Three Champion plugs fail on me in the last two summers- two suffered crimp failures and spit the core out on me, and one had a failed O-ring in the same crimp... all three were on different engines, none were IHCCs, but I've been told that the brand is known for that antic.