Gettin' there. Had to hurry out of work to get to Ace, got the tap, drill and cap screw. I was able to get the other rivet head ground off and got the plate off without removing the rivet, so it's staying put. Drill/tap went alright. I first tried just 4-5 turns, but of course, it's not pipe thread, so it started pushing coolant out when I revved it up. So I tapped all the way through, and bottomed the screw with a stainless flat washer onto the top of the block. I'm going to see if the Gasoila sets up any, and then try starting it again. I'm just wondering if I should use something else to seal it at the surface. Maybe even a crush washer or brass or something. Any other suggesteions? I suppose the cherry on top would be a cap screw with a tapered shoulder, and then taper cut the top of the hole, for a "tapered seat" seal. I suppose I always have the option of bombing it out to an NPT.
Edit - oh yeah, thanks to its proximity to the IP, there was no way to use a regular tap t-handle. So I did what will probably make most machinists cringe - used a needle-nose vise-grip as a turning handle
. Hey, it was the ONLY thing I could think of that would fit. And it did give me good "feedback" on how the cutting was going. I used bar&chain oil as cutting oil, to give the chips something to stick to it. Sometimes I'd get a full turn at a time, other times I'd feel it load up at just 1/8 turn. I've only had to tap threads a few times ever; it's def. one of those "zen patience" exercises, esp. in somewhat unknown territory as this.
Aaaaaand, the magic hidden number is..... A2U799736 - way up there, gotta be one of the last ones built. Well beyond the block heater issue threshold. At first I didn't see the 6 on the end, and thought oh crap, just five digits after the U. Closer look at the pic indicated something there, went back out, cleaned it up some more, WHEW! At least they didn't drill/rivet right through the original digits. So here's where it's at now: