512K boards are easy to find, and most 128Ks ended up either having a 512K board installed or the RAM being swapped to accommodate 512K.  Handy in 1985, not so much in 2014.  Finding a 128K board in there means you have to keep it as one, but it sounds like you've already decided to do just that.  These things are starting to become harder to find, and original boards even harder again.

Sockets will also devalue the board, so I would just stick with your standard chips.  The best solution is to replace them all as they will continue to fail otherwise, but if you are happy to replace them if and as required, you should be fine.

Nice work!