That's seriously ambitious (tips hat). There were a number of folks that came up with dual processor designs back in those days playing on the observation that most 8-bitters (and many 16- and 32-bitters) could never utilize more than 50% of the available memory bandwidth. There's an NS32000 application note somewhere that describes such a design, and NS had datasheets for an NS32132 that was an NS32032 with added some support for such a system. I dunno if the NS32132 ever shipped, however.