OK, here's the deal. The real Taito Arkanoid boards do not have a dipswitch selectable cocktail mode. It is a separate ROM version (code ROMs are at IC16 and IC17), protected by a microcontroller (IC14). So you need to swap the two EPROMs and the 68705 microcontroller.
Here are the chip labels (for IC14, 16, and 17) you are looking for for the cocktail boards:
Arkanoid cocktail (US): 20, 18, 19
Arkanoid cocktail (World): 20?, 22, 21
Tournament Arkanoid cocktail (US): 38, 37, 36
I don't know of any good dumps of the microcontroller code (the chips are protected, and not easy to crack). What is in MAME is just a hack... they just go around the protection, and they've dummied up the microcontroller data (so the pointers to the level data are correct). So don't try to use those to program a 68705 for a real board... it's not going to work. And the MAME driver for Arkanoid is a bit of a mess, particularly around the ROM versions, so don't trust what you see there.