Bucket seat track spacers

The earlier seat tracks like 66 model were 2 piece with slots where angle/heigth adjustments could be had if you were willing. They were a real pain to alter. In 67 that disappeared in A-body (still found in others like 67 Sport Fury) and plastic spacers under the tracks would provide these adjustments. They aren't really required unless you want or need different from level.
The only tip is be sure the spacers are same count and or thickness at locations or the tracks will bind.