New 3 point seat belts

Matt's got some good points as does everyone.
I recently purchased the book of assembly plant drawings for 67-9 a-bodies. The drawings confirm that '67 front shoulder belts were attached to rear seat belt anchor points. Looking at at the convertible drawings now, '68-9 'verts continued that practice. So that would suggest that at least with these models, the sides were not reinforced and a weaker location as Matt2000 was saying.