A man convicted in the attempted murder of a man who later became the boss of the New England Mafia is set to learn how long he will spend behind bars. Enrico Ponzo, who spent 16 years on the run, including a decade as a cattle rancher in Idaho under an alias, is scheduled to be sentenced Monday in US District Court in Boston. Prosecutors have recommended a 40-year-sentence, saying that Ponzo, 45, is a ‘‘vicious, violent, cold-blooded criminal.’’ Ponzo, representing himself, requested 15 years or less. He says he lived a ‘‘hard-working, selfless life in Idaho . . . as a stay-at-home dad’’ and community volunteer. He was convicted in November of several crimes, including the attempted murder in 1989 of Francis ‘‘Cadillac Frank’’ Salemme.