Mine has a 5 groove barrel, though from what I have read, some post 1950 LB No.4s were made with 6 groove barrels. My wood is some variety of Walnut and from the ones I have seen it looks like LB stuck with Walnut though the end of production. If memory serves 1956 was the last year of production at LB.
I will try with some pics, but can make no guarantees while. I can take a decent picture my computer skills are not the greatest.