Just now getting back to this, my latest project. Trainman, thanks for the advice. I have a gimpy bore light that usually doesn't work, so I'll probably just get a new one before I try out your advice. I have a small bright flashlight that I might see if it will work.
I did the next best thing, though. I have this big old Craftsman two-headed mallet -- one head's nylon and the other head's rubber. The dang thing's so old, the rubber head is just about as hard as the nylon head. Anyway, I decided there's one way to tell for sure just how bad that top tube is. So I smacked it all over with that mallet's rubber head. Immediately, the condition of that top tube became apparent -- which is to say, hmm . . . terminal. After smacking that tube all over, it stove in most of it. So next I took the mallet to the down tube -- it rang like a bell. I'm taking that as a good sign. The seat tube and the rear tubes also sang a bit in their own way, as did the forks. So, I'm seeing all this as good signs, although I will still try and do the bore scope inspection as well.
Next, I'll check around with local bike shops and see if there's somebody local that they use for the sort of repair I need. Then, failing that, I guess I'll look up Andy Gilmour. I have an automotive paint sprayer outfit, so I can paint the frame, if need be.