Seat belts on a original bench seat setup

[wolffcub]

I got the 3 point kit from Brothers a while back and just installed it yesterday. I says that the buckle strap is to be bolted to the floor under and snaked up between the bottom seat cushion and the back seat cushion. After doing that the snaking of the belt makes it way too short and just 3/4 of the buckle shows in the seat crack.

Has anyone else installed this kit and have any suggestions or comments. It does not seem right that the belt is this short.