Good idea for a conversion to update the model, but I feel the need to point out that the body is too long: the M4 was based on the Half-track Car M2, while the Italeri kit is of a Half-track Personnel Carrier M3, which was about 25 cm longer, or 3.5 mm in 1/72 scale. You also seem to be using the fuel tanks (which are of the type used in the 75-mm Gun Motor Carriage M3 and 81-mm Mortar Carrier M21 half-tracks) as the front lockers.