seat belt question

[stockgp]

i have two different sets of shoulder belts. one has three mounting points - floor b pillar and the rear cab wall. the other has two mounting points - floor and b pillar.

i've figured out how the three mounting point seat belts go in, but the driver's side is broken. i've tried to get the two mounting opint belts in, and they just don't seem to fit the floor pan.

i've seen pictures on here of other trucks that appear to have the same belts, so i believe they are from a c10.

so my first question is do the floor pans change through the years? maybe that's why the second set don't seem to fit?

second, the po put buckets in, but they are not bolted in properly. i haven't checked the front, but the back brackets just have some random looking bolts stuck in the holes. i can lift the back of the seat up and basically roll it forward if i want. how are they supposed to attach to the floor?

for reference, i have a single cab 76 long bed