I’d run the Hera Arms SFU with the MDT Skeleton Carbine stock. Certainly not an inexpensive option, but would be solid and keep with the “compact” theme of the sentry stock.
I had looked at the MDT a bit and have a email in to them. Ya its only going to be a 16.5" barrel in 22br....first barrel anyway, Borden Mountaineer action and bottom metal still up in the air