Thank you all. At least I have now progressed through jigsaw fret coping jewellers etc, all of which appear to have flat single-sided blades. I was just onto "Abrafile", and noting online comments as to unavailability of blades, when that was suggested. 50 years ago my Dad had a powered jigsaw, reciprocating circular blade, and a small table with a keyhole that the blade went through. I will next check out "Laser".
If I still had access to CAD . . . Replicate shapes and send out for laser cutting. Simples. However . . .
Task: 3 sections of hurricane deck. 4 mm wide surround on each (to be done in sections) from 3mm ply.
I had thought that with a powered 'abrafile' section blade and a 'shoe' table cutting would be more controllable.