Interesting find Tordoc. I think I actually looked at that model when it was at Profiles, but missed that detail. The foam-cast Raiders are very crude - especially after some abuse on the stage. Lots of dings, bad seams, and mismatches covered up by Plastruct channel and bits of tape. That additional gun barrel thingee might actually be.......... a pour stub. I've seen some photos of that same area (in the trench, under the gun) and there is evidence that something was there in the casting, but snapped off. The resulting "wound" (so to speak) is round and has the texture of foam. It appears that the master pattern was molded and castings were made, after which additional kit parts were added. Maybe those "stubs" were supposed to be guns and they just came up with a better one? Or maybe it was a pour stub and they just forgot to clip it before they sent the model off to Monogram? Who knows......
Gene