Ralph Castro was a student of Prof. Chow and then came to the mainland. He did work with SGM Ed Parker of American Kenpo to put together a system to market (but he was not a "student" of his).
Like Kara-Ho Kempo, I think that his Shaolin KeNpo (not to be confused with Villari's Shaolin KeMpo) is a snapshot of what he learned from Chow with some added chinese style forms to round it out.