Yes, the oval base at the bottom, later model towards the end of their engines. Thank you, curiosity satisfied ;-)
Does this make it more or less sought after?
I suppose it depends on what you are tying to acquire in your collection. If I didn't have this one, I'd likely be making you a offer (we all like a good deal, right?). But if I was just trying to get a model or two, I'd likely be looking for a pre-50s Empire. I'd image most members here know I have a soft spot for Empires (and that's putting it lightly) and I nearly have the whole line of their Steam Engine/Accessory line. In my collection the later #43 is my least favorite as the quality and craftsmanship isn't near a pre-50s B-43 / B-30 / etc. That is just my opinion and that didn't stop me from getting a #43 like yours in my collection :-)
The
#43 with UL Oval bottom I have came with the Empire paper tag and it is only slightly in better shape (no dents) than yours.