meanwhile, back at the farm...
I did stop at the shop yesterday on my way home and they seem to feel - as I did that the panel has to come out . They did confirm the rivets, adding they had a special tool(rivet gun) for it - one that allowes them to position the guard rail at the exact distance needed from the roof - ( for a correct fit for the seal) and yet narrow and long enough for the tight fit between top of car and upholstry . So I guess it will go there, rather that a DIY. these guys do know their business.
thanks again for your help and guidance