By late spring 1971 Jaguar, Rover and Triumph were grouped together under the Specialist Division banner because of this internal re-organization within British Leyland, the project was given a new name: SD1 (for Specialist Division). At this early stage of development, it was obvious that the new car would use the ex-Buick V8 engine that had provided service in the P5B and P6B models and would have gone into service in the P8 model. Extensive work had already taken place on this power unit in order to produce the required power output for the larger P8 model and it was logical not to allow this work to go to waste. Obviously, now that Jaguar occupied a unique and prestigious niche right at the top of the Specialist Division, there would be no requirement for the 4.4 litre version of the V8 engine to be used, but even that did not go to waste, finding its way into the Leyland-Australia P76 model as well as the Australian version of the BMC/BLMC Terrier truck.

In July 1971 and after much engineering development work, the SD1 had reached the full-scale model stage and when Management viewed the project, they were very impressed with the designs that were being mooted. It was at this point that the styling was yet to be finalised by Bache, but the British Leyland board gave the SD1 the green light for production on the strength of what they had seen so far. Not only had David Bache been working towards the five-door hatchback that the SD1 eventually became, but he also pushed forwards on a wilder proposal, which incorporated gull-wing doors – a concept that he believed was a viable one, but which his colleagues around him were not so sure of. The gull-wing idea was dropped on cost grounds, but not before full-sized models of his idea had been built. In later years, when he was in the position of head of Product styling for BL, he attended a designers’ conference, where he was still keenly trying to sell the concept to anyone that would listen.

One thing was very evident on the Engineering front for the new car; the range of engines available for the new car was very limited. Obviously, the V8 engine was settled, but the question of what to power the smaller engined versions that would be required to directly replace the Rover 2200/Triumph 2500 model was still unanswered. The then Current 2-Litre Rover engine was considered less suitable for use in a ‘seventies executive car, being as it was by that time, a rather unrefined unit, so it was deemed that the 6-Cylinder Triumph engine would be used.

As events transpired, the plan to add a overhead camshaft head to this unit was dropped when it became obvious that the straight six required more extensive development – and so, a practically new engine was developed in its place, the Triumph unit acting merely as a starting point. As it happened, this would prove to be an excellent marketing ploy, as Executive car buyers were becoming increasingly demanding in their tastes nothing less than six cylinders in their wagons would do. No consideration was given to using the Austin-Morris E6 engine, as the spirit of rationalization had not yet entirely taken hold at BLMC – whether it was a suitable engine anyway was debatable because in twin-carburettor form, it produced only 110BHP. However, in an in-line application, the ‘1750’ stroke could be applied to the E6, giving 2622cc. This is what was used in the South African built SD1, as well as in some of the Australian P76 and Marina models. An engineer who went out for the SA launch admitted that the 2.6-litre E6 was much smoother and livelier than the ‘Triumph’ SD1 engine.