Oh for it to be held on with screws! It’s the most awkward one to remove out of all my locos, but I have sussed it with 4 bits of plasticard or cocktail sticks. It’s the lack of bits on the chassis to hold on to that got me. Still it looks fine now, if not quite up to the original level of detailing. The replacement parts are sturdier anyway, and the other two will stay as they are.
They did have a thin lip around the headcode panel and the plated over ones appear to have a nice piece of sheet metal work which fits over the lip and is secured to the front of the loco. The design of the Heljan headcode box actually makes it easy to reproduce, though technically the existing headcode box surround should match the curve of the front. I didn’t want to file this down and respray the front and it looks close enough keeping it flat.
Here’s the current work in progress. Needs the yellow touching up around the headcode panel, lenses, MW equipment and a light weathering to complete.