Hi, Michael – its beginning to look as though you want to build one
Sorry, your link is not at all like it. Basically, apart from the suspension upgrades, which as I understand it came from some company uprating Imps for racing (Stiffer shorter springs, stiffer shocks, changes to the various suspension arms to give better camber angles, etc), the car body was modified by entirely removing the rear window panel and window, then extending it back following the line of the roof. I think this was done with a piece from another Imp roof, because the new rear window posts looked identical to the original rear window posts, but now came down to the back of the car. (I hope that makes sense). The roof addition was welded across and blended in to make a single smooth curved line from front to rear. The original rear cross member of the car was still used, and a panel added above it which was welded to the rear floor of the car, and the new window posts. This still allowed the engine to be removed as per the original. The panel which had been removed from the original upper rear of the car (supporting the opening window) was refitted into the new rear window posts/roof, and welded in place with a rollbar immediately under the inside edge of the roof (under the interior roof lining), presumably to add strength, and the original opening rear window fitted. The new rear side windows were fitted between the original rear window posts and the new ones (darkened perspex – very chic in those days!)
The interior was completely gutted, and recarpeted with new heavy carpet, and all the old original synthetic plastic 'leather' replaced with real hide. The instruments were replaced with electronic digital types (speedo, petrol and temperature gauges, and a digital rev-counter and oil-pressure gauge added) mounted on a polished wooden dash (a la Jag). The electronics for all these used TTL logic in a metal box fitted under the dash, (no processors then!) with a plug-in lead connecting to the digital displays on the dash – in those days, they were all 7-segment red LED types. I understand that basically the original sensors for various functions were used – for example, the petrol gauge sensor was effectively a variable resistor operated by a float, so a varying voltage from this was converted anolog-to-digital, then used for the display, so not particularly complex. It all seemed to work OK, I never had problems with them, and the garage had no problems accepting it for MOT. I gather the guy who built them used to work at the RRE, so it should have been a doddle for him!
As I noted earlier, the engine was the larger 998cc version, originally fitted with dual Stombergs as per the Stiletto version, but I later changed these for dual SU's, which seemed to be much better. I had some issues with the Strombergs very quickly becoming unbalanced, resulting in a (mostly) weak mixture to two cylinders, and a (mostly) rich mixture to the other two, and also an irritating 'hunting' effect when the engine was running at slow speed. I happened to have the SU's, (think they came from an old Jaguar 2.4 Mk2) so I stuck them on, and they seemed fine.
It didn't seem to involve a vast amount of rebuilding, and the resulting car looked quite neat – it certainly caused comment. I suspect that without the suspension upgrade, it may have been a bit of pig to drive, but as it was, it was fine.
As I said, I eventually sold it because I needed a larger car, and the guy who bought it crashed it, which was a pity.