First off, I am experiencing these machines far out of their temporal context. So maybe these were common at the time. For me, it is a first.
Snagged this 128k Mac for a low price. Ended up having 512k RAM. I opened it up expecting to find a 512k motherboard, instead I found this:
The machine had also been upgraded to support an 800k floppy drive. I'm a little disappointed that the machine isn't stock, but it came with an external 400k drive so that helps a little.
Added some photos.
Note the obvious alteration to the solder joints here - the RAM was removed and replaced with socketed 32k chips.
This is likely (I am not informed enough to know for sure) what the hand built circuit on the 128k board is supposed to be.