Is that an encrypted Z80, like the one the used on other 8-bit sega games?
Look at this file in the MAME source...
http://mamedev.org/source/src/mame/machine/segacrpt.c.html103 List of encrypted games currently known:
104
105 CPU Part # Game Comments
106

-?

Buck Rogers unencrypted version available
107 315-5010 Pengo unencrypted version available
108 315-5013 Super Zaxxon used Zaxxon for known plaintext attack
109

-?

Super Locomotive
...
123 315-5069 Star Force game by Tehkan;
same key as Super Locomotive 124

-?

Pinball Action game by Tehkan; also has a simple bitswap on top
...
It looks like it might be the encrypted Z80

However, the table above suggests it might be the same as Star Force. And there may be enough info to consider make an unencrypted ROM set to use with a standard Z80.
Paul.