Without presuming to tell Peter what he should do, I'd suggest figuring out a single-processor solution to this task, unless, perhaps it gets too burdensome to handle with one, and I don't think that is likely. The 805x will support external logic, but, with associated costs AND performance requirements both low, it's reasonable to use an MCU in place of some logic.

However, if there's a CMOS MCU ... ANY CMOS MCU ... including, perhaps, a 68HC11 (I'm NOT advocating for that, but ... It just happens that I have some components in that series that have enough pins ... ) or whatever, type, for example, that has enough pins to do all the work, it's likely it will use less power than two MCU's with external logic.

The problem one wishing to build a prototype or any other onesie, is in the packaging and the ease of using the high-pin-count parts in a onesie. There are adapters that allow those high-pin-count parts to be adapted to a 0.100" matrix perf-board as commonly is used in prototyping, but with various pin-counts, pin-pitches, etc, it's not easy to find the right adapter.

This is a prototype, after all, and not one likely to be headed for commercial production, unless Peter decides to make it one.

RE