When I started i had an 86 2wd 1/2ton short box Sierra that is now 4x4 3/4 ton with regular length frame so I need to cut and shorten it so my box will fit but I'm not positive where to cut it out at. I think it's just behind the cab but not sure. I've got it all together other than putting the box on basically. Any suggestions would be appreciated. First picture was when I bought the truck 15 years ago....second picture is what it is today.