I don't think you should try and keep your shins vertical if you're squatting with oly shoes and a narrow stance. If you've chosen that stance ideally you've done so because you're a quad squatter. In that case there's no need to try and restrict shin movement.
As far as losing the heels and going wider, you can get pretty wide and deep if you're flexible enough. I used to squat relatively narrow, in oly shoes and I made the switch to chuck taylors and a wider stance and was still able to hit IPF (USAPL) depth. It just takes practice and flexibility work.