The beds from 47 to 87 are the same dimensions. Where they differ is the front side panels where the steps mount and the rear cross brace. AS long as you take the bed with all the same year attachments (fenders & steps) it is pretty much a bolt on.
However if you want to use a 73 up bed on an older model or vice versa, the bedsides where the steps mount is different. the 73-87 do not drop as low, so you'll have to modify it for the older beds. to go the otherway you will have to shorten the step mounts.
I did the board writeup on how mine was done taking an 84 bed and making it work on my 70.
http://67-72chevytrucks.com/vboard/s...d.php?t=123833