Welcome Chuck,
There's a few things to look for but I'll answer your question first. I believe discs should both be round. I have never seen an "U" shaped disc on any post war truck. There may be more experienced folks on the forum who I'm sure will chime in if I'm incorrect.
There are a few other things to look for and I'm sure you have. While we're on the subject of the discs they should be to two piece variation. The earlier Lackawanna and some of the early Virginians had one piece discs. Inside there are metal tabs that hold the light bulbs behind the headlight lenses, in the 2341 they both should be straight upright without a bend toward the lens. Also, by the time the 2341 was produced I am pretty sure the battery cover no longer had any printing on it.
Keep in mind though that Lionel used every part until it was finished and some were interchangeable so if they found a hidden stock of battery covers, coupler discs, light holders, etc. they used them no matter when it was. Also, they shipped parts to their service stations so if a piece went in for repair it would be possible for it to come back with a part from an earlier or later version (both coupler discs fit all of the FM's). Like the battery cover.
The issue of fakes with the 2341 predominantly revolves around the shell. That's where you have to be most careful. All of the mechanical parts were interchangeable but it's the shell that matters.
Good luck. I hope it's the real deal at a fair price. I had the other 5 versions (just sold them) but have not been able to get my hands on a 2341 at a reasonable price.
Mike