Hmmmm.
Mortars fire generally high-angle, Howitzers mid and 'guns' or cannons fire low angle.
Mortars are short range devices, Howitzers are mid range and 'guns' or cannons long range.
(I'm trying to envision where you want to go with this.)
Mortars sit on the ground - stable, absorbs recoil well.
Howitzers on the other hand generally have wheels for fast transport.
So what would the blend look like?
Wheels - perhaps.
Barrel length of howitzer length and yet with the abilty to shoot at high angles.