56 Longbed to shortbed

[TNBandit]

My 56 3200 series has the shorter of the 2 longbeds 123" wheelbase. I know about cutting 9 1/4" out of the frame just behind the cab but I have read some things about needing to cut some off the rear of the frame as well. Is this only needed with the extra long beds or will I have to do this as well. If so how much needs to be cut ? The rear fenders come almost to the end of the bed sides as it is so I can't imagine having to cut anything off the back but want to be sure. Here's a pic.