The value of the POTs is really irrelevant, they could be 10k or 100k and still work the same if you want to go that route. The only real issue you'll run into there is that the controller is calibrated to the sticks that are in it, so you may need to fiddle with that some so the center and end points all work correctly.
What you want to do is possible, but that's going to be an extremely crippled wheel when it's all done. Racing games like Forza distinguish between a controller and a wheel controller, so some options and layout aren't available when using one versus the other. Also one of the best things when using a wheel versus a controller will be gone when doing a hack like that with a controller, the Force Feedback.
If I were going to hack up a $1k+ ECCI wheel, I'd at least get one of the XB1 wheels that are out now and use the guts from it versus using a standard controller, both for the FF and any firmware upgrades later on that the wheel may support.
If you don't care about the FF or want to drop a few more bills on an XB1 wheel to use for the transplant, you can use a controller, but it's been done before on every other system to date and the results are never as good as even the crappiest wheel for the same system.
