I have found this photo online (see citation), showing a Triumph Spitfire MkIII (1300ccm), as far as I can tell, completely stock, small 3.5 steel wheels, bumper, windscreen and a normal ride height. The rear axle on massiv negative camber in the typical "tuck in". Only the origin of the photo, the bumper on the door and the driver's helmet let you believe, that this car, in this spec was actually taking part in a race.
Notice: It is not a Apal hardtop, as written in the source- fuel filler is in the center - is is therefor a Sebring Hardtop - looks like a William and Prichard hardtop, but fitting for thelate bodied MkIV or 15oo Spitfire.. It is rarely seen, since most of the fastback hardtops were made for the early body (Mk1-3).
A very interesting picture, although raising a few questions. A TR4 body (at least without TR4A trim) but what seems to be a 6-cylinder engine. Most notable of cause the fastback hardtop fixed and a lot of the inner body panals cut away. Therefor it is not a hardtop as such, not properly removable, That's why it's called GTR4 by it's owner.