The flat top gas block is another option. If you go with the flat top and use it to mount a folding front sight, you'll have to find a taller sight that's made for mounting on a gas block. The gas blocks don't line up with the top rail, it's slightly lower.

Is there any way to post pics of your new rifle? My first thought when you said BSA was maybe it's a PSA, they even sell factory blemished lowers. They are functionally perfect, but the laser engraving isn't just right or the anodizing isn't evenly colored inside and out.