I myself dismantled a perfectly good 89 sub for a newer drivetrain and front clip for my 74 Blazer. Usually you can pic up a sub for a lot less money than the same era blazer. I got my 89 for $1,500.00 and have everything needed to make my 74 updated to 89 fuel injection and newer front sheetmetal.
If I tried to buy all this stuff in pieces I would have spent way more than $1,500.00. A lot of people don't like them because they are too big and somewhat of a pain to manuver.