Credit Management system for Mame Arcade

I am looking for a circuit design for a standalone credit management system in a Mame arcade. Circuit will receive a swich input and keep count (up to 99) of the ammount in a pool. Then when another switch is pushed it will remove one unit from the credit pool and active a switch to credit the Mame system. The display is driven by Nixie tubes (NH-12A to be specific) and will be driven by K1551D1 (74141)'s so I need output to work with those components. Links to help you understand some of the terms and equiptment here. Mame [login to view URL] Nixie Tube (Nh-12A) [login to view URL] K1551D1 (74141) [login to view URL]