I figure the 19 spline is from the 3/4 ton vehicles (pickups, and "station wagons") as referenced in the Dana/Spicer document. One would expect the 1/2 ton lighter duty versions to be more common.
I have only seen one other 19 spline scout axle; a friend it used in several project vehicles. I told him that scouts were 27 spline (I have used their lockouts & hubs for years on Jeeps) but he showed me different. (I know it was a Scout because I helped remove the body from the frame (god awful heavy SOB).
Several years ago I also helped with a custom pickup that was built on a Travelall chassis; it had a Dana 60 flanged rear axle and 19 spline front stubs with flattop outer knuckles. The Spindles on the Travelall were the IH 8 bolt pattern and I would expect that they would interchange with Scouts.
I believe that these scout oddballs are conversions done by previous owners to get stronger stubs.
P.S. here is a link to Dana/Spicer x510-8 you might want to save the document as it was difficult to find a working link.
(EDIT) the Warn aplication chart
Lists 19 spline lockouts for IH 1/2 ton pickups and travalalls with a manual lockout (9072) specified for the 1/2 and 3/4 ton pickups.