Bear with me because I have only owned one motor (Johnson 50hp 1975)Friend is offering to sell me '88 merc 80hp. Other than attempting to mount it on the transom,how can i tell if it will fit current boat (1975 starcraft 15') with johnson long shaft, i believe 20". Also, how is a Merc 1988 as far as quality. Asking price is $700<br />Thanks!