Not so much of a silly idea as an exercise in self-inflicted pain and suffering (and finally, a little joy). The old (soon about a hundred years) Airfix defiant doesn't really have a single thing working for it; it's seriously undersized, has no real detail and has only the vaguest resemblance to the original. This was a recent boxing with very shiny, but usable decals, so I opted for the day-fighter colour scheme. 

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To make the model into a somewhat more decent representation of the original, I used the wonderful drawings and the detail pictures in the Mushroom Publications book on the Defiant. The kit needed to be a lot wider, so it was beefed up with a thick slice of plastic card between the fuselage halves. The too small tail fin was built up in the same way, and the miniscule turret was replaced with the top turret from an Airfix Halifax (which was the same type). I scratchbuilt the interior of the turret and cockpit. The oil cooler under the nose was replaced with a vac-formed one, as was the cockpit canopy and the turret top with open doors. The wheel covers and wheel wells were made from plastic card, and the undercarriage was mostly scratch-built. Incredibly, the wings and tail surfaces were mostly usable.