I get that you can order parts and put them on a car , even vastly improve it.
Getting back to the "Taxi" though, I think its at another level.
Example.
Lets take NC Engine builder whom I guess by his handle, builds engines for a living.
Give him all the parts to assemble a Magnum 408 stroker engine.
Now, give all the same parts to a Hobbyist.
NC will build the better engine with more power at least 90% of the time because he's more experienced, knows all the power and tuning tricks and, has done this so many times , he knows the weak and power losing areas of the build.
I think the Taxi is at the level it is because of this type of experience and knowledge supplied by Hoschkiss and the other suppliers who helped build this exceptional car.