Bud, I really appreciate the reply,
I went up top this afternoon and here is what I found:
the vent stack is just "slipped" inside the steel pipe. The outside rim of the stack just rests on the taper of the mounting which is flashed to the roof.
From your reply can I just plug this tapered mount? or are you suggesting I leave the stack on the mount and some how fasten and plug that?
The other thought I had was I wondered if there was something I could do to convert it to a crawl space vent, but I do see your point.
In any event, I just pulled the stack off with ease it's just sitting there unfastened. The insulation cylinder lifts right out. I could probably just lift that entire thing out from the roof, by just me or using a helper.
The steel pipe, however, seems fastened somehow, seems like you said, it's in the floor joists somehow. I can wiggle it side to side fairly easy but I cannot lift it out, it seems pretty heavy.
I see your point if I could just get the flange off to get my ceiling back, and it doesn't fall down, yeah I could cap it and cover it back up. But this house loses heat something fierce, and I'd just prefer to have an uninsulated alley way to the roof removed. I know it's more work, but by doing this I can also get 3 feet of closet space back from the upstairs loft as the false wall was installed to hide the pip stack.
again thanks for the reply, I can post more pictures if you have other ideas.