Hi Guys,
Here is a link to the step-by-step guide on how I made a new Union Pacific flat or blunt end cap: https://ogrforum.ogaugerr.com/topic/how-to-create-a-new-flat-end-cap-for-your-18-union-pacific-dome-car?reply=105888697105001761#105888697105001761
Lou1985, my new observation end cap has not been permanently mounted on a car yet, so I will test fit it on a Lionel extruded aluminum passenger car to see if it fits there body also. It should fit... but I will take a photo and let you know for sure.