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I don't know if all 73-87 are compatible. However, there are some welds at the rear that you'll need to cut and re-weld. They're in the tail gate area where the bed sides meet the floor. The rest of the side is just bolted.
I'm not 100% sure but I would bet yes. I'm sure someone will chime in with a definite answer.
Lowhoe, your question has been answered in another thread on this site just recently. It's in the Body section of the forum- http://forum.73-87chevytrucks.com/smforum/index.php?topic=27450.0
You do know there is a patch panel for that... http://store.73-87chevytrucks.com/merchant2/merchant.mvc?Screen=PROD&Store_Code=7&Product_Code=0850-135-136&Category_Code=7387Beds