Looking at the geography of some I these I am probably off base but did anyone find any so close to a moving body of water that a raceway could have been dug for a sluice in close proximity to the block?? I found of all things a drawing of a portable and smallish waterwheel that by it's metal construction brings it closer to date. Darned if it doesn't seem to bolt to the same type of base.
This next part is once again my guess per another piece I read. I will not purger the piece as I only use it for reference. It seems earlier portables, yes steam and fuel powered, operated and then were brought to preset foundations for their next go around. When these were wood the whole works used to shift with ground conditions, frost, etc. Now you get lousy and inconsistant cuts. While I couldn't see any reference to the bases, wouldn't it make sense that if you stabilized the saw you eliminate that problem ?
Now that would limit the block to the use of a saw only and not that multiple drive concept that Ben posted.
I am having better luck with the Info of my Grandfather's place being converted to a dress shop than I am with these cursed blocks, but that's another tale.
G.
Check this out, some cool stuff.
http://www.owwm.com/files/pdf/americansawmill/1910-americansawmill.pdf