Installing plywood or chipboard over 1X6 planking on a 52 year old house' roof.
A lot of variables, and I am not an expert, but, personally, I probably would go over it with 7/16" OSB. However, my suggestion to someone else is to either wait for an architect ot engineer to come along, or preferrably to contact one in your immediate area.
Just a couple of things to keep in mind though...
It is going to add weight, so the truss design should be considered.
Since you have trusses, which inherently transfer the load straight down on the walls, I do not believe that added strength is as much of a factor as it would be, as an example, on a 100 year old house with balloon framing.
It is going to add thickness, which could increase the labor, hence cost, in regard to flashings, second floor siding, etc., depending on the configuration of your home.
Also, and you have probably already looked at this, but this is the ideal time to take a serious look at insulation and proper venting.