As others have stated those kits are a real nightmare. The parts sprues on the earliest kits were “salvageable” but as the tooling aged they became unusable. The flash on the sprues became as thick as the parts themselves; it was basically a blob of styrene. It’s been a while since I modified any, but as I recall on the early kits the roof sat too high and had to be lowered, and the coupler pockets mounted the couplers too low. The bodies are a good starting point but that’s about all. If you have another option (i.e. resin) I would go with that. YMMV.