Seatbelts....
66 to my knowledge didnt come with shoulder belts. Just lap belts.
Cody and me went junkyard scroungin....and molested a late model suburban for its belts.
The floor boards of the 66 are at about a 45 degree angle.....so we had to level things out.....as late model belts work by inertia. The belt housing has to sit perfectly level, so that when ya smash the brakes....a little weight swings in one direction or the other and locks the belts down so that they wont lengthen....allowing you to go flyin thru the front winder!
I then mounted the top mount of the belts with big fender washers. This werent easy, as there was no way to physically hold the nut and washer with your hand. I had to glue the washer to the nut.....and then put the nut in a long box end wrench and slid er up in there. Took several trys.....but we got er done!
