Erm, I would say this is actually illegal ! As you dont own the ROMs or copywrite for any of the images, logos, music etc.
Im sure Wayne from Bally (Australia) and Gary Stern would soon put a cease to exist order on you, and I know Gottleib used to pull anyone hosting their rom files.
I was told that the 'Ultrapin' had a big license payment, and it didnt really have any 'theme' games like Twilight Zone, Addams etc....
I think if I was you - keep to selling the cabs, you may hit a lot of problems.