See, that's what I was expecting.
So, equill, you are saying in your ever eloquent prose, that all the Happy Mac signifies with 64K ROMs is that it found boot blocks it understood? That would suggest that boot blocks have a commonality between MFS & HFS (at least up to 6.0.4), in particular some signature by the Macintosh File Manager/Initialization Package, that tells it "I am for you Macintosh", which for whatever reason is the same between the two formats. Inside Macintosh shows that the first sections of the disk is an area called System Startup Info, even before it gets to the Volume info. However, it goes into no detail about this, presumably because it is proprietary date a developer cannot change.
So a Happy Mac means, "I'm OK and you stuck a recognizable Macintosh disk into my pie-hole"?