"The seventy-sixth man swims in the narrow, shallow river too."
Translation:A hetvenhatodik férfi is a keskeny, sekély folyóban úszik.
The is goes after the part that is also'd. It might be difficult for English speakers because English uses also & too ambiguously. The translation I see ("a férfi is") means that there are several people swimming, one of them is the seventy-sixth man. Yours means that the man swims in several things, such as the narrow, shallow river.
"is" at the end of the sentence: It depends on what is the rest of the sentence.
"A keskeny, sekély folyóban úszik a hetvenhatodik férfi is." is fine
A hetvenhatodik férfi a keskeny, sekély folyóban úszik is. well... this would mean he swims too, and does something else too