Hope something simple for you Debs - Bessie had a smoky cab because there was an oil breather-filter above exhaust which was dripping onto hot manifold and smoking out the cab[xx(]
Sorted with the wondrous tiger seal.
Just a thought, but if Skyes engine fairly clean already, maybe a photo of it from above if you can get one might be useful on forum, may give you a headstart Dozer if it shows anything up