Hi Daniel,
if you are aiming for a higher level of screen accuracy, MP40 pouches made of canvas are only meant to be worn on the shoulder. None of the sandtroopers seen on screen was wearing a canvas pouch on his hip.
Keep in mind that some garrisons won't even accept a canvas pouch on the hip for basic approval.
For the hip, you should consider a leather pouch, a so-called "Stolla Wien" or a Spanish pouch.
However, either way you will need to change the straps at the back of the pouch to fit the ammo belt. With the leather pouches I found it easiest to attach some new leather straps using pop rivets.