Richard: From your details, I think there is strong hope that your bike may be an Italian produced frame.. To my knowledge, the diamond shaped chain stays were not used on Mexico made frames (Anyone care to tell me I'm wrong on this?) The workmanship and lug shaping would be a big clue but an experienced eye would be needed there. Is that frame a 61 CM, c to c? Those Italian bikes were advertised as being silver brazed which was an unusual claim from an Italian builder...(No mentions as to percentage though.. 2%? Ha!) FWIW, I believe it was the Sanson team that used Benotto for a period (I always liked their jersey design at that time too!)
Dale Brown
Greensboro, North Carolina