Ethan,

All of this stuff has happened to me before... I spent a frustrating
week exploring the same things you are now & having the same
problems. 

I think there may be something wrong with the kernel in latest
miniroot... I had the exact same problems as you describe when using
it.

I finally had success using:
o latest bootblocks (3-8?)
o ultrix executable version of netbsd disklabel  
o 2-14 miniroot


Drew