I don't think you will find a -531 head in the US. I thought the -530 and -531 castings came out after the B21/B23 series, so even the most performance versions of those engines -- the B23E -- would have the performance version of the older head, the -405. Anyway, we never got the B23E in the US, but perhaps you could find one in Canada. I am not sure whether you would find a -531 head in Canada. I believe it was fitted to the performance versions of the B230 series, which never came to the US. Here, we had the 114 hp model B230F or the 160 hp model B230FT. I think some countries may have gotten a version called the B230K that had the 531 head (and a higher lift cam and more like 135-140 hp). I am not sure whether the B230ET with the A grind cam had the -531 head, but again, that was a non US model.

Philip Bradley