First that board bis both a horror and beautiful. ;)
The horror is that troublshooting a loose wire is likely unfun.
That and for many years it was told you must use short leads and watch
But the color and diversity of wires is art. Also a reflection of patience.
Plan A, use Arduino:
My approach to buttons and switches is elsewhere but one adopted is
using a common Arduino Nano as a loader host. While I may tire and
grump about finger pain of pushing buttons the Arduino will do it for me
willingly. Since there is enough flash in the Arduino I can have it load
the serial binload, tbx, or whatever.
Why do that? More people can program (as in insert code into the flash)
an Arduino with ease (free software and the nano or uno has programming
port). WHere programming a 2716 (if you have them) or any other part
(2732,2764, and EEprom parts) requires a more specific programmer
or homebrew hardware. Where a low cost nano has it and all you need
is a USB to microUSB cable and the free Arduino IDE. That and it
replaces the switches!
It is set up as 8bits of port as binary output and a few single pins to push
the load (DMAin) and load mode. The nice part is unlike EPRom the
loaded code is not resident so problem of address conflicts with eproms