I have a 70 B body, so I can’t speak for the E body, but I doubt the results would be different. I purchased the retrofit 3 point belts sold by Classic Auto industries and am very pleased. These use the two factory bolt locations. I don’t think the arm at the base compromises the belt in any way. Only two minor drawbacks I can see. The first being the belt retractor. It need a little help to reel in the belt when you disconnect. The spring could be loaded a bit tighter. The second is the height at which the shoulder section crosses my body. I’m 6’1” and it nearly misses rubbing my neck. I haven’t had a shorter person ride with me to see where it hits them. All in all, I’m a happy customer.