FWIW, I ordered the Happ 3-inch "High Ball" trackball, and I installed it last week in another prototype CP. I used the matching mounting plate and recessed it into the top surface of the panel. I love the ball being up higher than the usual trackball, because it's much easier to make fine movements.
Just something to consider when you're trying to decide which trackball to order.
OTOH, I find the "High Ball" too high for my fast play; my hand hits the closer-to-vertical side of the ball, hurting my hand and sometimes knocking the ball off the rollers.
FYI, I call my type of TB users "Panel level wackers" (my hand moves just above the top of the control panel to the ball), and the other major type of TB user "Ball top slappers" (hand starts just above the top of the ball moving down and sideways). But I don't say the names outload.

So it really depends on how the buyer uses the TB on which is better for him/her. (And how you're mounting the TB under plexi/lexan, or not.)
What size trackballs did Marble Madness use?
Atari "Midi Trakball" (aka 3" trackball) according to the manual (can find links from KLOV). (Atari "Mini Trakball" were 2-1/4".)