Oh it'll probably be pretty tight, but I don't think it'll be TOO tight. I guess it's really hard to say for sure without knowing the width. There's certainly enough depth.
Some people like to have all kinds of space around the trackball. I've found that I never need much (unless I'm playing Marble Madness). It all becomes a matter of preference.
While we're on the subject, there's no reason why the SF layouts can't be pushed out to the extreme ends of the control panel. It can be nice to have space below the buttons where your palm rests, but you really don't need much room to the left and right. On the contrary, this makes it easier for two people to stand in front of the machine at the same time, and makes more room for a trackball (assumign it'll fit at all).
Physically speaking... if the control panel is around 22-23" - it's too tight for two grown men to play a game of street fighter in front of. Fitting a trackball a joystick with 6 buttons each on a control panel this small almost always results in a control panel that can't be used very well. I've tried to do it... it doesn't work.
You'll want some room around the trackball. Sure, you may not use a lot of room, but other people will take some wild swings in bowling or Golden Tee. Since he said he wants to play as many games as possible, this is an important point to consider.
The reason they may not be pushed out to the edge is there may be clamps on the edge used to hold the control panel in place. That control panel has to be secured to the game somehow. It makes sense to push the controls out as far as they can go to the edge, but often times, the method used to secure the CP can get in the way (depending on the width).
I still say, and many of the veterans who have built before will agree, if the controls are too tight, they might as well have not fit at all. This looks like it'll be too small, but if the CP turns out to be 25inches+ he'll be ok.