The question is what American coach has proven himself to be a great marathon coach? Not many I'm afraid.
Of the post collegiate coaches who coach marathoners:
Mahon- tried him
Larsen- Meb's coach, in Mammoth
Salazar, Schumacher- Nike
Hudson- didn't work for Ritz.
Steve Jones- Did well with Torres, but heard the group disbanded.
who else is there out there? Pete Rea, Chapman, Scott Simmons?