First thing I noticed. Maybe that's the problem...
Marvel Mystery Oil works wonders for freeing up a seized engine. Worked great in my Saab.
It sounds to me like you were just hitting a compression buildup from the plugs being in. Perfectly normal.
You can look at the flywheel through the starter hole obviously, and I believe there is an area under the transmission where you can see it. I'd definitely like to see a pic of this starter, though.






