Tom,hope the pics below help to point out the difference between Monotype and Inglis ?

Barrels -


Sliding butt group/Lower -

Three pointers,machining to rear of the lower on Monotypes is MKI fashion with more material removed - marked in dark blue.
Machining to area by sear pin is different - marked in light blue.
UKicon F.Tibbenham butts have slips in the wrist of the butt,Inglis butts don't - marked in orange

ATB KG