After removing the piston last night, I had decided to soak the crankcase on the Bridgestone with a mix of ATF and Acetone. This seems to be an internet phenomenon when it comes to a cheap and extremely effective penetrating fluid. As it happens, the Bridgestone BS-7 engine lent itself to this treatment because the center portion of the case that the crank rides in seems to be completely sealed. There is even a tiny little drain plug bolt under the engine that drains just this chamber.
So I filled up this area with the ATF/Acetone mix and let it sit for about an hour. I intended to soak it overnight, but after an hour I went out just to see how much I could rotate the crank. Before the treatment, I got about 5-degrees of rotation by turning the cooling fan back and forth by hand. After an hour, I was able to get another degree or two each time I went back and forth. After a minutes I got about 45-degrees of rotation.
So I let it soak a bit longer, then was able to turn it over a full 360. I drained the old fluid, added fresh fluid, and rotate the crank over several times. After a couple minutes, it turns freely with a single finger's worth of "force" on the fan assembly. I snapped a few pictures.
Central galley where the crank rides:
Circumference of crank is very clean, with no signs of corrosion. The needle bearings on the big end were even shiny:
A bit more progress each day.