Thanks Daryl, Gordon.

I may have found a suitable combination.
I rechecked the rifling and the twist seems to be approximately 80"

Still using the .690 ball and the .020 patch, I upped the charge again and added a bit more TC wonder lube to the patch. Although the patches were lubed, they were still fairly dry to the touch.
Not surprisingly, they finger started more easily but It would probably help if I sourced larger patches as even 72 caliber patches seem easy to misalign.

I upped the charge to 110gr of ff pyrodex and the first two shots were to the sights at 50yds and the third shot increased the group to 2". I would not be surprised if the rifle groups within an inch at that range with this load.

I fired at 100 and it shot flatter than I expected only dropping around 3 inches.

I am sure that will require more experimenting.

Tom