The Blazer floorpan changed in '78, that is, 73-77 floors / seats are different than 78+.
I can't speak as to whether Burb or pickup seats would fit a Blazer of similar year, not having owned enough of them. My first guess is to say that the floor pans between each of the three types (Blazer, Burb, pickemup), so the seat *brackets* at least will differ, if not the actual seats.
However, I would suspect that in your instance you should be okay. You can verify this with a quick check with the measuring tape and, as we say, the "visual inspection" -- look at your truck, look at the other seats.
-- A