dhc-5
T/Tops
The requirements to convert the aircraft is listed in the Type Certification, however this would not be the problem if you wanted to attmpt this.
The problem is the historical records to confirm and qualify the life limited components. As most aircraft were military controlled many civil authorities will not accept these records.
5A (civil) aircraft have the same powerplant and propeller combination as the 5D and the 5E. Differences are airframe mods obviously removal of the military equipment and addition of equipment for civil requirements.
Engines props are civil certified and airframes with a suffix "A" after the serial number are civil certified.
cheers