References

Plans: 'Modeller's Draught' 40ft Coastal Motor Boat

Articles: Model Shipwright 96 '40ft Coastal Motor Boats'

Books: 'Fast Fighting Boats' by Harold Foch

'Torpedo' by Roger Branfill-Cook

Example: An original 40' CMB under restoration at Duxford

And of course the internet, where searching will lead you to all sorts of information and other photos and diagrams

of not only 40' CMBs but the 55' versions which were made up until WW2.