Not sure about positioning the mounts, but you might want to rethink the seats...
Harnesses don't really work when they go around the seats, ideally they need to go through them.
I found that when I had mine going around the outside of my seats the upper parts of the harness were constantly trying to slip off over my shoulders. If I leant forward I'd slip through them and headbutt the steering wheel - not much use in a crash
