Got it home today, a few boards swaps from my collection of no less than 4 complete stacks! and its works perfectly. Just needs an RTC chip to complete and a very good clean :0 very happy.
According to the info on Jed Margolin's site, you can just get away with buying two of the cheaper zeroram chip, the only difference being the clock function won't work. But seeing as the clock on HD/RD only goes up to 1999 (as I found out) that's not the end of the world. High scores, championship laps and control calibrations will still be saved.