Train museum in Henderson:
I'm a member of "Friends of the Nevada State Railroad Museum".
If what you're talking about is what I know, it's in Boulder City, not Henderson. Don't know about anything in Henderson.
Last time I was there (year and a half ago) there was no museum.
They have a storage shed where they do restorations. I don't know if they offer tours.
They do run an excursion train for a few miles (3 1/2 miles) from Boulder City to Railroad pass (they stop before the tracks cross over the highway -- it's right behind the casino there at Railroad pass).
Here's a website: https://www.nevadasouthern.com/
Website says they're closed until February 3rd
Here's what the website says: "There are currently no indoor interpretive, exhibit or display facilities at this location."
I will add, I've found railroad people to be some of the friendliest around. If you show up at the maintenance facility and ask to look around or for a tour, they might let you. Even better, e-mail in advance and see if you could arrange something. I've been invited up into many a locomotive.
It was a nice little trip. While you're in Boulder, there are a couple of other reasons to be there. First, there's a nice cafe for breakfast in downtown Boulder called the Coffee Cup. It's got a seriously good chile verde omelet. There's also a small brewery in Boulder.