I spent many days, and several attempts, to create SCNN drives so that I could convert a Surya into a FR-1900 Quilen Class frigate.
I have created numerous Klingon comercial and other non-S Graph type engine nachelles for use on arious projects.
I reasoned that Klingon non-millitary vessels and such would utilise technology form subject races or of simpler , lower performance and cheaper technology. Also, in order to control essential commercial and infrastructure space flight inside the Empire, many drives would be non-anti-matter Warp systems, using Fusion, Impulse, Neutronic or some other low yield power source.