Can't find thread about shortening long bed?

[bmfm64]

I've been searching for 2 days to find a thread I saw about a month ago on how to shorten a 67-72 long bed. I've found a bunch that simply say to take 12 inches out of the front and 8 out of the back but there was one I found before that was alot more detailed. Anyone any better at searching than me? If I remember right the box was blue and it was being done in a driveway. OR if someone can just tell me that works too... if I remember right, it also mentioned that you have to remove a specific cross bar from the floor and it told you where to measure from as well. I don't need frame instructions as I'm starting with short frame I simply can't find a SWB so I'm gonna try my hand at chopping one down. Thanks for any help.