Well, I contacted Summit Racing, explained the situation, including that I had bunged up the MSD starter somewhat, and they told me I could return it anyway. Them's is good people to deal with...
So I got the ACDELCO starter back in. I sure have gotten a whole lot of experience replacing starters in a very short time.
Got it wrapped up with a heat shield all nice and purty. I checked the clearance between this starter and the primary header tube and there is a good 3/4s of an inch clearance there. So that MSD starter is quite a bit larger in diameter than the stock starter is.
I can't believe that I haven't read ANYTHING about anyone else having clearance problems between the MSD starter and headers. Even with brands other than LG Motorsports, I can't imagine that there is going to be that much difference in clearance issues around the starter. There really just isn't a whole lot of room to play with there. And looking at this from another angle, I can't believe that MSD wouldn't have designed the starter with headers taken into consideration. What's the chances that someone would put in an aftermarket starter and NOT also have headers in their car?
The passenger side header went in very easily with the ACDELCO starter in place, so that is in and all bolted up now. Connie helped me by holding up the tail end of the header while I got the bolts starter. I think she likes being on the creeper underneath the car. She says it feels cozy there. I had the car on the lift just high enough for her to get under the car, which stands underneath the lift arms for safety. Then I had to put a step stool next to the engine compartment so I could reach in and get to the header bolts. Awkward, but doable.
Anyway, got the ignition stuff back in too, and all the wiring dressed up neatly and protected from the heat from the headers. Did a test crank of the starter, and even with the fuel pumps disabled the engine still tried to start on me, as some cylinders were firing off. So the car appears to be tired of being on the lift.
So I just have to put the exhaust pipes between the headers and cat back pipes back in and check for exhaust leaks and I'll be back where I started trying to zero in where that intermittent drive train noise is coming from.