Beech Duke VH IFD was operated by Kevron Aerial Surveys during the 80s. Also Queen Air CTE saw service with Kevrons at the same time.
IFD had a large aux tank fitted into the nose compartment (240l from memory).
We flew it to Asia a number of times and when full of gear and fuel we were always appreciative of the curvature of the earth for takeoffs. Whilst it looked like it was doing 100 mph standing still it was one of two aircraft ( the other was an Islander) that when the throttles were closed for landing the drag forced you forward into your straps.