There may be a GT6 available, with a good/repaired chassis already stripped, but it is quite expensive for a donor car (I know GT6's go for a lot more then Spitfires), but this seems expensive for a chassis, engine and gearbox (basically as I would replace all the other bits with new).
I would like to go down the Straight Six route and have rotoflex, so I may have to bite the bullet.