In the 1960's Lionel sold a train set with a car that carried two Mercury space capsule. I have this car but it was missing the capsules, so I printed a couple. The model was actually from NASA at "https://nasa3d.arc.nasa.gov/search/friendship/". I converted the 3ds file to an stl and scaled it to fit snuggly into the car's support holes.
The model lacks some of the original capsules detail but it is a NASA model so the scale is correct.
Note the stl file is mislabeled as"Gemini_Friendship_Capsule" - it is actually a Mercury capsule not a Gemini capsule.