how to replace keyboard with arcade buttons?

Well, one guy in town came up to me and asked why I use arcade buttons( the midi fighter) and naturally I just told him that its because they feel amazing and they're super responsive. He says he would love to try something with the arcade buttons for a month or two and I would love to give him my midifightersss- but i need them. So i offered him that I would take his USB keyboard and transform it into like two midifighters. His keyboard looks like this.



and I plan on making something like this



I put the keyboard there just so it doesn't go to waste and now he doesnt have to touch his laptop.

Now i thought this would be a fun project- especially since he is paying for everything except the enclosure which I am making from some wood laying in my garage.

now the only thing I dont know how to do is solder the arcade buttons onto the keys. I know how but i dont know where is really what i should say. Here is a picture of the insides...









there is another keyboard I can try or is it easier to just take two numpads? cuz i believe there are 16 buttons on each one. Right?