Tops

[bouncytruck]

Double wall tops bolt on from under the bedrail, single wall tops bolt down from above the bedrail. The bolt patterns are different from what I understand. Single wall tops also have dome lights so you'll need the pigtail in the truck if you want them to work.

Blazers didn't start production until 1969, so it'll be tough to get your 72 top to fit a '68. Singlewall tops were not introduced until 72, but not all 72s had single wall tops (consistency wasn't one of Chevy's strong points back then).