i thought the e15 gear on the end of the shaft had a different profile and number of teeth for the internal gear on the a12 so the e15 gear had to be removed and the a12 dissy gear welded/fitted on. The e15 aslso apprears to be 10-15mm longer in the shaft.
Im going on the info given to me by the guy i bought my dissy off, he modded it himself (it might be a n12 dizzy though not the n13 series one).