“BTW, “ALL”,the main bolts that attach the entire caliper assy. to the vehicle are locked too: Had thought of removing the entire assy. to get better access to the caliper pins, but, no such luck.”
I recommend removing it anyway. It’s how I remember doing it. And don’t use a flame under a car unless you are absolutely sure you can do it safely.
As for what you’re attempting: use a pick or sharp pointed chisel to scrape away any corrosion, dirt at the base of the heads, clearing a path for the penetrant to get to the threads. Good luck
That’s a good point about flame under a car.
The main bolts are really locked up too... And this was a garage kept vehicle of which my mechanic buddy said the lack of visible corrosion was remarkable. But these pins / bolts have been a real bugger for me, compared to past vehicles I’ve worked on.