Rectangular Watch Case 3D Redesign

I’m shifting an existing round-dial watch case to a sleek rectangular format and need a solid 3D CAD model that preserves all internal clearances from the supplied STL while upgrading the exterior look... (Budget: ₹600 - ₹1500 INR, Jobs: 3D Animation, 3D CAD, 3D Design, 3D Modelling, 3D Printing, 3D Rendering, 3ds Max, Fusion 360)