converting the default rubber dome stems to mx stems wouldnt be hard. Although it would be tedious, painstaking, and possibly suicide inducing.
here is my thought.
buy a cheap set of mx key caps.
step 1) grind out original rubber dome stems. grind it smooth, but be careful not to grind through the surface of the cap.
step 2) remove the sides from the mx caps so only the typing surface and stems remain.
step 3) glue the remains of the mx cap into the rubberdome lid.
for the circuit board and switches,
step 1)use a QUALITY set of digital calipers and take copious measurements of the case
step 2)design circuit board in Eagle or KiCad. this is where you use all those measurements
step 3) send the design file to oshpark, or whatever pcb manufacturer you prefer.
step 4)wait a week or so for your pcb to arrive
step 5)populate pcb
step 6) clearance all the holes in the case to allow switches room to pop through.
step 7) button it up
step
step 9) profit
estimated time to completion: 8 months.
estimated cost: $600 USD