I could be wrong, but maybe you are thinking about this wrong. First, to have even power pulses and to help maintain balance of rotating assembly, 72 degrees is actually the answer. If concerned about spark and valve timing, that would be adjusted on your camshaft and distributor.
Have you consulted Google for drawings to see what has come before? I think for something like this, there is no reason to "re-invent the wheel". I doubt you have in mind any major improvements for performance or reliability. Just copy what others have done.