Your diameter mesurement seems to be of curved lens of projector unit. That is not the largest diamter on a projector unit:
I would at least used low beam HID projectors - it makes them alot easier to sell in a few years.
Be careful to select such a small turn signal. They will not be easy to see for oncoming drivers at a distance. That is why DOT regulations requires 60mm diameter turning light.
If you lack space in headlight, consider mountign highbeam in a differnt location. It would be advantages if u mention the brand/model of car, mayeb even a picture.