OK, the task is actually accomplished.... The starter is out of the truck! The secret is: in the procedure manual it showed that indeed, the dipstick tube "Oil Level Indicator Tube" removal was part of the process. Getting that out involved removing the starter and shield bolts, getting it tilted out of the way, and using a zip-tie to hold the oil pressure sensor wire to it so that it was also clear. Then, I used a good old Mapp gas torch to heat the snot out of the boss in the block where the tube fits, while my son yanked/twisted/wiggled the tube from the top.
Other than a hot piece of junk landing on my lower eyelid, the operation was a success. Tube removed. I'm a little concerned because the o-ring was not on it when it came out. Either it stayed in the block, or fell off after the tube was out? I may fashion a small hook to see if I can retrieve it. Once the dipstick was removed, the starter could be moved around and pulled down far enough to disconnect the wires. Not the easiest wrenching session, by any means. But finally successful.
Curiously, the main power wire which connects from the solenoid to the starter stator wiring was completely broken. Makes little sense, as it is not under any strain or tension. A bit of corrosion, causing excess heat when power was passing through, and the wires melted apart? As good a guess as any....