[jabborabbo]

So...I take the truck to a mechanic that has experience with these wonderful trucks, and he declares that the manifold leak is causing the knock. I take the truck home, spray the manifold bolts and studs with Aerokroil over the next three days, remove the bolts and nuts without breaking any of them, replace the old gasket (pic below), put it all back together - the knock is gone! The truck runs fine! I’m a very happy guy!

VWNate1 - I have no doubt that I’ll need to do the engine work you suggested at some point, but since I bought the truck from the original owner and it had believably 113,000 original miles and he was an 84 year old retired anal retentive engineer that kept meticulous maintenance records (the guy GREASED that truck on schedule for crying out loud!) AND kept it in a garage while he owned it, I figure that it’s never been run low on oil - the guy believably said he never drove it past 60 mph - so I probably have several tens of thousand miles left before I need to rebuild that engine. Plus, and more importantly, the wife and I just moved to another house and she’s wanting to move all our crap to the new house and I need a truck to do that, so....

Thanks to all for the advice!