Overall, it's the same game featuring six stages of action and a story line that continues in the sequel Calvary Class. I've made and MP3 which worked on my real ZX81. There is a few seconds delay after the game loads as it sets up the screen. I made it with a collapsed screen to save load time.
The MP3 is at:
http://www.mediafire.com/file/a26hpwbuw ... C.mp3/file
Here's the emulator file And some screenshots
It was interesting revisiting something I programmed in my twenties. I may have learned a lot since then, but it's still a pretty good game. I was a decent programmer even then.