Anyone know what make this is?

It looks like Pola. The trucks may not be original.

You might try typing in CM&SP 5907 into the internet.

Here is one showing different trucks:

@Hot Water posted:

What does this have to do with 3RS modeling, per the explanation at the top of this forum?

It didn't so I moved it.  By the way, the pictures is of a Pola produced flat car.

I think Lionel used Pola molds for their line of Standard O boxcars, flatcars, and gondolas.

Pola made the tools, with one-piece Bettendorf-style trucks, 'scale size' plastic/metal axle wheelsets and horn-hook (like some HO) couplers.  At first Rivarossi / AHM marketed in Europe and USA and they worked fine on 2-rail.  There have been comments over the years on the models' slightly smaller size and FWIW I've always had a sneaky feeling that the boxcar ends have a flavour of South American or Canadian prototype?

The replacement 3-rail truck sideframes shown have the bolster ends visible, don't know if or why the manufacturer (K-line??) had to do that.  Some other 3-rail cars had this style too.

Jason

Thanks to all who commented.  My apologies for the incorrect placement.

Pola flatcar with Lionel frame.  The Lionel frame fits the Pola car without any problems.

That's started as the Pola underframe.  If Lionel fitted their own trucks maybe they altered the bolster area which we can't see under the truck in the pic.  Or just added a spacer for 3-rail?
Jason