I've been following your thread and everyone who posted had valid ideas. Now you've added a bit more information to the mix. My own thoughts originally leaned towards a radiator in need of rodding or replacement.
You may very well have a blown head gasket but the smoke you describe is typical of worn rings and/or valve guides and/or stem seals. I don't think I've seen you mention a compression test anywhere. Before yanking the head off I'd at least do that--it should show up a blown gasket--or worn rings and the plugs may show evidence of one or the other. A blown head gasket (or cracked head--as I found on a Saab) will sometimes cause a cloud of white smoke (vaporized coolant) on cold start-up-- a symptom to look for.
My point is -- if you take the head off are you prepared for the down time if the valve guides are bad?---or the rings? What is the point of changing the head gasket if it is not actually the problem---better to save that gasket for use in a motor rebuild--which you will be looking at some time in the not too distant future if the smoke is oil.
I'd install the replacement radiator, set the timing properly (does the advance work?) and see what you've got now. --- (lazy)Dave