You'll notice when you get to the level where they swoop down and attack you from the side. You need to be able to move up to avoid them and not get killed.
+1 on the Ms. Pac-man conversion. That's what I did with mine. Bonus info: Gaplus CPs and Super Pac-man CPs are exactly the same layout. So if you have a hard time obtaining a Gaplus CP, grab a Super Pac instead. (You could always drill the holes needed on a Ms. Pac CP, but why destroy it? You need to swap out the joystick regardless to an 8-way Midway stick).
Here's my cabinet. I should be finishing it up this summer, fingers crossed!