Happs sell both varieties of trackball.... The PS2 version and the straight optical encoder version that will have to be attached to an IPac, or Turbotwist or some other encoder. (trackballs are cheaper from Divemaster or Ponyboy on here)
Not sure why you don't want a spinner..... How are you going to play Tempest, Arkanoid, TRON and whole raft of other games, without one. If you get the "Turbotwist 2" from
GroovyGameGear.com then you will not need another interface for your trackball either, as the interface that comes with it can accept X,Y,Z inputs. You connect the spinner to one of them and the trackball to the other two.
As for trackball mounting, some people put their CP overlay over the top of the mounting plate which is recessed into the surface of the CP using a router... Other people have it on display on the top surface. It's all a question of what you like to look at.
Best Regards,
Julian (Fozzy The Bear)