and...SUCCESS!
I received my SCCs today. I cut out the old one, and, indeed, one through-hole via was not electrically conductive! I had to actually drill through it with a drill bit and a pin vise. Once that was gone, re-soldering it was a simple matter. New SCC installed and soldered. Bam! Started up, no issue. Connected mouse and external floppy so far - works fine. Included RAM chips are 1 MB each, I know that now. Well, thank you to EVERYONE who helped figure this one out. I hope that it will inspire others to repair boards that appear too far gone. I also started coating the traces that were exposed with green liquid electrical tape: it looks just like the original coating in color and makes for an awesome repair that looks original!
Stay tuned for the restoration of the rest of the unit.
SCC hacked out. Look at the crud!
Here is the through-hole via. The one right in the middle that looks crusty.
Cleaned and ready to re-mount:
New SCC replaced:
Up and running!: