Is this a question as to how to make it look realistic and weathered? If so, I'd start by looking at as many pictures of the real thing that you can find for reference, I'd also go to Forgotten Weapons on YouTube, I think that he's reviewed a real WWII 2.5" bazooka on his channel before. If not him, then I'd check out out the channels of WWII reenactors who might have a real decommissioned one shown in one of their videos. This will not only give more reference, particularly for size and scale, it would also be very useful as a weathering guide.