Have to say you would do really well to ask if anyone has got half an electric seat from a jaguar/rover 800 (not quite as stupid as you may think cos people buy them for the Bosch 35w motors they come with.)

They come with a few linear actuators in them (to move the seat) with some mounting brackets which you can weld/bolt into place. Probably going to be a lot lighter than butchering a car jack.

You can then play about with it at quite minimal cost (Seat with motors is normally around £25)

Andy