'74 wellcraft 20 fisherman specs?

hope it's ok to ask a question about a 20' fisherman :-) I'm wanting to repower from an in-line 1974 150hp merc to an '05 150 saltwater series merc. my "spec" plate is unreadable. can any one out there tell me what the max hp on this hull is?? i am concerned about the new (?) hp ratings and heavier weights of these late model engines. anyway thanks in advance if you can help. ps great forum here!!
larry