Mine is still doing fine with it's 500 rear axle. Handling is much less choppy but you do need to use the 500 springs.

The original 169 springs feel rock hard but the 500 springs drop the back end down too much.

I used the spring top rubbers at both ends of the 500 springs and got a nice level ride height with the 500's more compliant suspension.

The standard 169 wheels fit comfortably inside the wheel arches even though the axle has moved outwards by 25mm at each side. I have not measured up the 100HP wheel clearance but suspect the axle would be too wide if you have wider wheels.