That is very interesting Ken, and maybe it would work for the tapered rafters I am not sure but for sure it would work for shorter pieces.
Splitting out cedar fence rails is not an easy chore, especially with the cedar that we have growing now, the old rail fences were split from the large hollow red cedars that abounded in the early forests but are now long gone
I did run across large split threshing floor planks in one of the earliest barns around here it is a swing beam barn, and had floor planks that measured 36 inches across, that had been split from large pine trees, and were 20 feet in length.
It must have been quite a chore to have split them from these huge trees with what they no doubt had to work with in the 1700's
This same barn had waney roof board that were also 36 inches in width, and vertical sawn, these marks were quite noticeable, so immediately it dated the barn to the early 1800's, before circular blades came into use at least around here, even then they couldn't have sawn that large a log.
The large vertical blades that were 6.5' to 7' could easily have sawn these large logs--slowly--for sure--but steady!, theywould have been run by water power, usually a barrel wheel, not a turbine! there is quite a difference.