Bryce,

You are right... the speed switch provisions for the D50/80/Classic 1CR's Rug Renovator will not jibe with the speed switch for models 516/Sanitronic VII. While some may find it tempting to disable the speed switch on these machines so they run regardless of whether or not something is attached to the front of it (so as to allow these single-speed Kirbys to accommodate the Rug Renovator), I would not recommend doing so for the sake of your machine's value.

I recommend you try finding a D50 or D80 to go with your Rug Renovator.

~Ben