[cooperhw]

Rutt Rowe,

I cut 60" out of my wheelbase and about 10' off the back (after axle). Are you saying I cut off too much?

Just kidding.

The 12" off the middle takes the frame from a 127" wheelbase (long) to a 115" wheelbase (short). The 8 inches off the back just works as this is up under the bed and keeps it from hitting the back rail when the bed goes back on.
Like said earlier, "it's been done a lot, and these numbers work".
Google shortening a long bed. There are videos of Stacy on Gears doing it. I watched those videos quite a few times before my first, and have since done a few more. Works.