The following is a general look (no specific production period) at the sealants applied to the undercarriage panels and brackets on a 68 San Jose Mustang and Cougar
1- Rocker to floor pan seam.typically the worker applied the product with an applicator (gun) and spread the product to attempt to seal the seam as instructed. Normally we find most of the product on the floor panel and less on the rocker lip. Maybe a 90/10 or 80/20 split
Normally starts behind the torque box area and at the rear it stops at the front edge of the rear spring front mount panel. There are examples where the worker applied more produce (for some unknown reason) and ran the sealant across the front edge of the floor and rear spring panel or straight back to the pocket behind the rear spring panel along the rocker panel
2- Front seat inner belt anchors. Sealant was applied and spread with a much wider wipe than the rocker sealant. Sometimes it was heavier other times lighter/thinner or not so complete around the bracket
3- Rear seat inner belt anchors. Sealant was applied and spread with a much wider wipe than the rocker sealant. Sometimes it was heavier other times lighter/thinner or not so complete around the bracket. Often appears that the same hand applied the front and rear seat belt anchor sealant
4- Rear seat belt anchors. Not sealed with sealant. These two examples support that and show one car where the area lacks sealant and the other where the rear wheel well sound deadener was applied so that they area was covered with that product
5- Rear wheel well lip. Before rear sound deadener was applied a application and wipe of sealant was applied around the outer edge of the outer wheel housing. Difficult to see or take a picture of - I've highlighted over the remains and signs of the sealant in the first picture in the second to indicate the area covered. Pattern is approx 1/2" wide around and above the lip where it bends horizontally
6- Trunk drop to quarter panel weld line. Sealant was applied and spread typically from behind the quarter drain rearward horizontally not normally following the edge reward and upward
Hope this helps explain what I've found on unrestored 68 San Jose cars