Looks Spitfireish to me, but an early one. MKIII maybe? Don't remember the big hole in the top of the chassis on the MKIV (though it has been 20 years).
careful not to overgrind when finishing off the welds - flap discs are much more accurate and gentle than grinding discs.
Yeah it is a Spitfire its a '76 1500. the pics are of the underside of the passenger outrigger. There was a big rust spot where the outrigger joins the chassis as well, thats the next job, apart from that the chassis is sound (which is more than can be said for the one on the car which has been sat in a field for 7 years!!) Pics are of the replacement chassis I picked up from e-bay for £50.