...That's how the OP walls were built, depending on your 'insert panels between. Then finish it off with trim'...
On this one you may have lost me...???...
"That's how," reads like absolute statement of certainty...???
I'm fairly certain, as a working Historic Restoration practitioner, that none of my in Europe...and North America (including myself)...most certainly...could not...make a statement like that about a period home of the circa date?
Craigdarroch was built, as you stated yourself, in 1890. In 1890, for such estate homes of that cast of society the modalities of construction where original in context. That would indicate the means, methods and materials for such architecture would be traditional hand tools, and approach modalities of working the materials. These original methods of construction for such panels are fairly well outline in a number of text predating its construction and still used today in there restoration, as was the case with Craigdarroch.
I agree it "could be" done many different ways to replicate a "faux" version of it, yet that is not how it was most likely done at all.
"Rules of Work" (and additional guidance) for this time period covering Panels, Architraves, Moldings, Stairs, Doors, Windows and all manner of instillation was still set down by references (still used today for restoration.) These, of course, built upon even earlier systems of work based even more deeply into means, methods and materials of traditional understanding. Some of the most common references (but not limited to them at all) of the time (still used today) for Craigdarroch would have been:
The Carpenter and Joiner's Assistant...
By J. Taylor, 1810
Practice of Architecture...
By Asher Benjamin, 1833
Civil Architecture: A Complete Theoretical and Practical System of Building
By Edward Shaw, 1836
Carpentry and Building, Volume 14
By David Williams, 1892