They are different in many ways. E.g., it seems that the B series had the carbs mounted on the left side (on the GT6 they are on the right) and a PO had 'made them fit'. The linkage is also different, the fast idle mechanism is different, the needles are different. Not sure about the jets, those might be the same. There's no S/SE stamped after the 150, because there's not even a 150 stamped onto mine. They just read Stromberg CD. I put some pictures up in the past, they are here: https://skydrive.live.com/redir?resid=4AC03D6F1EC8F583!2819. (Note that I have since moved to throttle return spring to a more sensible location.)