how to get hp/capacity plate

[Keywest18]

ive been remodeling a 1976 correct t16 boat and i dont have the hp/capacity plate. i have the hull id number and even contacted the company but they said they dont have anything going back that far.i know alot f guys go to trophy shops and get them engraved there but im trying to find out how i can grt a max hp rating for my hull.the guy that re did my transom said it could handle a 115 even though it had a 50 on it. i had him go overkill incase i added a jackplate i wanted it to be solid. my plan is a 60-75hp which i know the boat will handle but i dont know what kind of trouble i would get in having a boat with no hp/capacity plate