Sorry, that was a typo, I gets stuck at the question mark, not the Happy Mac. And the question mark isn't flashing. I just tried Lido again and looked at the partition map. A driver is installed. The interleave defaulted back to 1:1. Being 700 Megs, it's modern drive, so it probably has i's own cache. I'll try and repartition the drive with a boot volume of 40Ms and see how that goes.

As far as the ROM, bug, that's probably no it. I found an Apple support doc that stated they only produced about a month and halves worth of machines with that bug. This is a Platinum Mac Plus, so it shouldn't be of the same vintage as those Macs effected.