After his time in the military, Montero had coaching stints as an assistant with the Pacific Tigers (1945), at Salesianum (1945) and St. James High School for Boys (1946–1948).

After a brief stint with the VMI Keydets, Montero returned to Salesianum and served as head football coach from 1956 to 1965, being highly decorated while leading the team to several undefeated seasons.

[4][5] In addition to his success as a football player, Montero also won the Philadelphia Catholic League shot put championship three times straight, including defeating Bucko Kilroy in 1937 and Frank Reagan in 1938.

[7] Montero received several athletic scholarship offers, with one newspaper noting that he was one of "the greatest tackles ever turned out in the Philadelphia Catholic League".

[8] He enrolled at Pennsylvania Military College and immediately became a starter for the P. M. C. Cadets football team at left tackle.

[10] In August 1939, it was announced that Montero had signed a deal whereby he would join the professional Wilmington Clippers if he did not find a college to attend; however, he ultimately entered La Salle University and played for their Explorers football team that year under coach Marty Brill.

[15] He reportedly was a selection to the Little All-America team and had an offer to play in the National Football League (NFL) for the New York Giants, before he was called to serve in World War II.

[12] Montero was stationed at Stony Field in South Carolina from 1941 to 1942, being a player for its military service football team and also its coach.

"[3] Montero had shrapnel in his back, stomach, shoulder, and by his eye, and spent a full year in hospitals recovering.

[3] Montero began his coaching career with the Scholastic All-Stars, for which he played, in 1939, and then was player-coach of the Stony Field team from 1941 to 1942.

[13][16] While he was recovering from his wounds from battle, Montero assisted in coaching the line for the Pacific Tigers under Amos Alonzo Stagg in early 1945.

[37] He was considered to be a very talented recruiter, with one team staff member saying that Montero could "pick up a rock and find an outstanding football prospect.

"[2] A notable athlete he recruited was Randy White, who went on to be a Pro Football Hall of Fame player with the Dallas Cowboys.