Well 6/8 and 4/4 are more closely related than you might think. 12/8 and 4/4 are virtually interchangeable, and so 6/8 is pretty closely related to 2/4, which is like a half bar of 4/4. For this reason Yamaha seem to use 4/4 as a fundamental unit in many of the styles labelled 12/8 and 6/8 and so it might not be the mess that you think - just try it. You can't do any harm.
Mike