Great setup using the gunners from the 105 to man the mortar.
Historically, Artillery used to man the mortars, not infantry, especially in siege warfare, like in the 18th & 19th centuries but in the 20c with trench warfare in WW1 and mobility in WW2 the mortars became an infantry weapon.
Interestingly here in Australia over the past decade, with changes in technology (and funding), the Reserve Artillery Batteries have lost their field guns/howitzers and are now only equipped with mortars! The wheel goes full circle !
John