Besides wanting to add the buffer chips in a low profile out of the way fashion, I was also thinking to make a few other small changes. Presented here for your approval.
-Add some power on LED's to top of board.
-Add a DB-9 foot print over top the .1" matrix of holes, if the space is needed for a chip, it can be placed over top the DB-9.
-Add the buffer chips, but keep them as close as possible to the edge card connector, thus allowing maximum space for prototyping.
-Redo the silkscreen so there are lines in a grid of 10 by 10 holes (presently, I think it's 20 by 20)
I'm not sure if KiCad can be switched to a manual mode to allow such overlapped pattern of components/holes. Time to learn.