Right L18_B110. I've been doing some searching and I've found just that.

The early Roadsters (1.6L and smaller), the GX Hitachi's carbs and at least some of the 510 carbs were 38mm (1.5"). The Z's and 2.0L Roadsters are 46mm (1.75"). That number comes straight out of the part number: The Z's are HJG46W (46mm) and the early Roadsters are HJB38W (38mm). Still trying to figure out what the "B" and "G" mean - there is also an HJL which is a 510 "flat-top" Hitachi.

So in short, my 240Z carbs will not fit on a GX manifold unless I bore the manifold. I've also found an article arguing against putting the larger bore carbs on an engine smaller than 2.0L (http://www.jetlink.net/~okayfine/su/zsus.html).

Well, for now I'm looking for some more details on which 510s' used which carbs to widen the number of interchangable parts. But in any case, I still dont' have a GX manifold anyway... still looking for one. BUt when I finish my "research" I'll post a more comprehensive report here, if anyone is interested anyway.

Michael