Here's the write up on installing my seat belts, with the pictures.
https://www.stovebolt.com/ubbthread...ve-improve-drive-repeat.html#Post1162006The mounting locations I chose have significant structure around them, so use the large washer or nut plate on the bottom as supplied with the belts and should be plenty secure.
Again, may as well use shoulder belt. Same details for the bottom mounting points plus one at your preferred height in the door pillar.