I would think an original postwar 2037 steam chest/pilot would be an exact match. I can't imagine Lionel would have changed the basic casting for the pink color in the girl's set. Olsen's shows the steam chest part number as 2026-54. tttender.com has reproductions of that part. But there are variations from the original issue. I'd contact train jeff at ttender.com'. He would know.
Given the part is a reproduction with modern paint, I'd just paint over the black with a rattle can. Take a pink piece from the set at match it to a cap of Rustoleum or Kylon spray paint. My first choice of sheen would be satin, then flat. But use your actually pieces to guide you on that.
If your not experienced with spraying ... there's a number of techniques various modelers use. Mine ...
- Make sure the can is room temperature or a little better. Sitting in the sun for an hour is a good way to warm it up.
- Shake 3 times more than recommended. I hold the can in the middle and twist my wrist back and forth. More efficient than shaking your arm up and down.
- Outside, a nice calm day and have a box to cover it after each spraying to avoid any airborne dirt/insects sticking to the fresh paint.
- I'd spray the bottom first. The top the next day.
- 4 extremely light coats 10 mins apart. Resist the urge for better coverage on the initial coats. They'll build to a uniform look. Time the coats. It only takes 1/2 hour start to finish.
- Shake the can between coats. Start spraying ahead of the piece, sweep past it and then stop spraying. (practice a bit before the actual piece).
- In the sun with a box over the fresh paint, it will begin to cure. But it won't be fully cured (e.g., hard) for a week. Be careful not to scratch it until cured.
Freshly painted, it will look out of place given the loco's current "patina". That may make you decide to do the rest of the loco. If that comes up, there's a few techniques for removing the old paint before spraying the new.