Well now I have found it, the blurb describes it as a Dellow MKVI from 1958 which had suffered damage and had the alloy body replaced by this fibreglass Falcon unit. The engine is a one litre pre-crossflow Anglia unit.
The issue I have is that I believed the MkVI to be Dellows last stand - it was not the familiar trials car but an attempt to be a proper 2 seater road sportscar, and as such it had a full width fibreglass body already. I