All about the engine
The critical element would be getting a 'reliable' engine/prop combination that could function long enough to see an airframe off the ground and back again.
It would not have to be used at max power or flown at max speeds and weight, but it would HAVE to be suitable to get 20 mins (at a time) of flight for demo purposes. The airframe side of things would be less of a challenge as the weight could be kept down and it is not as if is has to rocket Tanks and take flack. Their problem is the lack of available product knowledge re what are normal operating limits, but modern technology could help there with sensors assisting to pick up issues BEFORE they become failures. The all important gear train and drives can also be sensor protected to avoid running in a range that gives premature wear leading to failures. There is no doubt that the use of modern materials in critical components could also reduce running issues. Many years ago I took a serviceable exhaust valve* from a pre-war radial engine to a specialist provider of valves to the racing car fraternity for an opinion of its suitability. Without even going into detail of material they condemned the part as unsuitable and said they would make a replacement (that would never break). They did and they have never failed since and are now a common 'fix' on this type of engine. That is how I would approach anything to do with a Sabre, as we have some wonderful materials now that were not available when they were new.
* I used to suffer valve failure in the display world (and transits) which 'could' wreck the engine if not chopped immediately. During a display it was less critical because there was somewhere to land, but it was less than helpful on a transit in poor weather !!!!.
Decades ago Pobjoy was on a gliding course at Swanton Morley and a couple of the instructors had flown Typhoons/Tempest. During a break in flying the conversation got around to engines (and reliability) and the CFI related that you had to fine tune the engine by 'feel and sound' to find the best rev range for smooth running. Although the manual would give a suggested rev/power range he said it was only a guide as subtle change either up or down by a 100 revs would suddenly give a much smoother run, and then you used that for that machine.