Zeus, what is the condition of your battery? How old is it, do the terminals look to be clean, or have you cleaned them as well?

Your latest voltage output
>600 RPM and NO LOAD it was slightly higher - 13.96V
sounds much better with no load. Have you cleaned all of your ground connections as well, like body grounds? I know the electrical system has weak points, as I am still making discoveries with my 300E.

A new regulator kit may be in order for you though ( I would, after your succes on cleaning). Good luck