Seat belt bolts
Longer ones for the front retractors and shorter ones for the tunnel is what I'm thinking.
Back seat uses 7/16-14 though.
Front belts use 7/16-20 on the left and Rear belts use 7/16-14 on the right.
Seems odd that they used 2 different thread sizes. But this is in my 69. Can't say if they might have changed by 71 or not...