That was the problem I was running into. With 6.0.8 on both partitions, it always booted off of the first partition. I booted off of the floppy and initialized the first partition. At restart, I got a flashing disk, therefore it couldn't see the second partition for whatever reason.
The fix? I started with a 800k floppy drive and a 150MB internal drive. My spare 800k floppy drive turned out to be bad. I added a Super Drive never intending on reading 1.4k disks plus a skinny 40MB hard drive. I booted off each floppy drive for drill and both boot. I initialized both hard drives and installed 6.0.8 on both hard drives. Dual boot works great this way.
Next, I booted from an external 700MB drive and installed 7.5.3/7.5.5 on the 150MB drive. The install took about two hours. Yes, 7.5 is slow on this SE I know, but with 6.0.8 on the 40MB, it is the dual boot that I wanted.
Now, I just need to find a use for this machine. With two internal hard drives, it picked up some weight.