Irish man here can't help but the aircraft is
Sikorsky H-34A-SI Choctaw >
built as CH-34A >
Converted I believe CH-34C >
Finally converted to a S-58T
Manufacturers serial number 58687 US Military serial number 56-4312(N), Nicaragua Serial number: FAN518(YN), FAS-51(YN)
http://www.rotorspot.nl/product/s58.php
https://www.helis.com/database/model/S-58T/?filc=NI
Note that the number on a US military aircraft of that time should be read as 64312 = 56-4312
The first digit is last digit of fiscal year it was ordered/ bought.