Skinner engraving was done in-house. I just happened to be looking at Skinner engraving Saturday. Very poor quality. No depth control. Templates irregularly sized - the "I" was taller than other letters for example (by quite a bit). (Opus 890, 1932).
The following picture shows the font. This example, engraving clearly done more carefully than the preceding, does give a bit of an idea of the irregularity of depth, however.
http://database.organsociety.org/photos/NC/Asheville.BiltmoreEsta.1995JAllenFarm.20130913.093130.jpg