Somebody actually put the rifle layout in the right direction the first time
Swap the black box or magazines with the brick of ammo, get as much weight as close the hinge as you can. This will also help with the balance as you have the CG of the rifle off center from the handle. Keep the heavy stuff from migrating towards the rifle and scratching it up by putting it underneath the rifle in the carrying position. Rifle should be on top of everything with scope up when you close the case and grab the handles. Purpose of this exercise is to protect the rifle, carrying anything else is a bonus secondary objective.
Since you got the right tool to properly cut foam without heartache, this will be much easier to do. Once you are happy with your layout, mark it with a sharpie approximately 1/8" smaller than the objects on all sides, this creates a tight fit that retains your stored items. USE some quarters and put a few half circle cutouts along the lines so you can fit your fingers past the foam to pull out items. Use a strong overhead light to cast shadow for easier tracing with the sharpie pen.
An electric 2 oscillating blades kitchen carving knife works well to make fine adjustment cuts after the hot wire has done it's job. You may or may not want to "V" angle cut some of the cut-outs to make it easier to insert and remove items, but straight cuts usually work pretty well.
For the block box and F class bipod you may want to make them sit vertically and cut 2 layers/pieces of foam in a narrow slit to save layout space.
Linear Mode
