Shoulder Belts

[eyebuzz]

Hello,

Curious about installing three point seat belts. See photo below - the plastic plugs are just behind each seat - all three rows.

1) These are for the shoulder strap, correct?

2) Do these just pop out? screw out? (I'd rather not ruin them to find out)

3) Are there threaded nuts under them ready for the aftermarket shoulder belts available or just a hole in the sheet metal?

4) How easy to install the aftermarket shoulder belts? (at LMT, Classic Part, Brothers)

Thanks,
Tim