So I took a good hard look at the exhaust today while she was warming up to go home (yeah, in 80-degree weather, she still needs a minute to stop chugging and sputtering)...
Since I changed the oil using some Mobil-1 10w30 and about half a bottle of Lucas synthetic oil treatment, it has turned from a white/grey to a black, but only lasts until she stops coughing and wheezing... The exhaust system is extremely sooty, so it may just be blasting out 37 years of soot and carbon... I haven't pulled the plugs again yet, will do that tomorrow and report the findings. Also, I plan to hack the muffler off near the axle just for a "is this thing getting too much backpressure maybe?" test... It has a cat for no reason AND an oval muffler, and I've noticed a lot of dents in what looks to be 37 year-old exhaust piping... I was also tempted to hack it off at the y-pipe (cat is about 1.5ft from the y-pipe), but that may create more carbon monoxide in the cabin than desired...
The perceived knock is a definite knock, but what's really strange is it now only happens when the engine gets hot (after extended driving), and it sometimes stops when I turn right? o.O
- CK