The front end was dragging along the floor with the supplied yellow springs/shocks correctly fitted and had zero suspension travel Swapping them for red ones from my Porsche resulted in the car riding as it should. The red ones from the [Decool] Porsche have a greater amount of compression resistance.
The yellow ones I put on my Porsche, and the front ended sagged.
Comparing images of hard and normal shocks, the yellow's that I received do not have as much spring material in them. Replacement harder shocks to be ordered from Bricklink.
Re the shifting mechanism, I may revisit it in the future when time permits but as the set will almost certainly be a shelf display, I'll probably not bother :)