To be honest I really had some thinking done about this. As the HC has a box construction at the inner sill there's not much space to make new mounts. Also the seats gets a bit high for my lenght.
So... I cut away the box, and as I wanted to be seated in center of the steering wheel I found me BIG hammers and made some new shapes to the floor.
I used the seat mounts from Gummy the Chevette as (i'm not a professor but...) these seemed to be the same as in an HB and fitted the seat mounts perfect.
Before (right side):
After (left side):
Test fitting the seat: