Thanks for all the replies. Certainly a fair bit of time and knowledge put into them, and they are very much appreciated.
I'll weigh out my options, make some comments on some of what I've read above, and answer some of the questions asked.
On the 79TA, I bought it new in 1979. I'm in Canada but it has never been winter driven. It was stored outdoors for at least half of the time since 1996. Throughout the 80s I made a number of changes to it. It original came with the 403 Olds, but at some point I switched it to a Pontiac 455 (maybe 73??) I still have that engine sitting around, separated into complete block, heads, and intake separate. Right now it has a 400 Pontiac in it, maybe 76 or 77. (It's been awhile)
I had been hoping to find oil in it, and hopefully get it started, before I started putting any money into it. Hope has changed.
What I managed to scrap out of it with a small wood bit was light tan in color and very fine, little bit of wind blowing under the car and it just seemed to blow away. Certainly that wasn't a heavy residue.
I had removed the plugs and sprayed Fluid Film into the cylinders, but never attempted to turn it over to this point. And turning it over is on hold for sure. I had a bottle of Mystery oil in hand at Canadian Tire, but not sure if I bought it or not.
I had considered doing a kerosene or diesel flush, and considering I already ran a couple of litres of new oil down through each valve cover, I may do the flush anyway. I don't mind the waste of time and a few dollars, but wouldn't do it if there's a good reason not to and this point.
Not the end of the world I guess to pull the engine, I have a fairly heavy hydraulic engine hoist that I pulled a few BB Pontiac engines with back in the 80s. That might be as contaminated as the 400 though.
I'll look at all the areas suggested for rust out.