I'd listen to Tokyo, they are local, sprintex are not.

In all honesty i think you're crazy - end of the day, you may be permitted for the blower, and all the peripherals, but if a cops having a slow day, they can pick you for anything.

As for insurance not covering it, i dont know where you got that information. If you use an insurer that caters to our crowd (shannons for example), they will add your modifications to the policy, and increase the sum insured in line with what you've spent. Permits, engineers certs dont come into the equation.

But hey, its your time and money, do as you please!