Listed below are the Revisions for 3.01 and 4.0. I also have a feeling there may be a difference in the pop bumper sounds in the later revisions ??? I'm not 100% sure but think I remember something about that.

The empty slot is fine, just needs the C5 ROM. When updating you also need to change the Display ROM.

Hope this helps

(Tommy fanpage on Facebook https://www.facebook.com/pages/The-Whos-Tommy-Pinball-Wizard-Pinball-Machine-Data-East-1994/147739828633855)

Version: 3.01
Release Date March 28,1994

* (J-22-29) "4 Engine Start" bug

* (J-22-38) MYSTERY not available during MBALL started by MYSTERY

* Left Eject will try to start a U.J. feature if M-BALL is ready but
not ready at the L.EJECT

* Game starts immediately even if balls are missing

* (J-22-44) MYSTERY LIT is displayed correctly after 99 ramps

* Trough correction for when outhole is intermitment and balls fall
back in

* R_TOURNEY is now not tested upon START of game, instead R_RESTART
is the only test made

Version: 4.00
Release Date April 6, 1994

* (J-22-50) Pinball Wizard Ramps score for the duration of PINBALL
WIZARD

* Extra Ball buyin for .25

* Italy Coin dispenser