omc engine and sterndrive i.d.

[Thunderbirdone]

I have a 1979 bell boy with a 120 omc (GM) engine and a omc 400 sterndrve. The number on the sterndrive is serial number, w193036 and the model number is 981871. On the motor there is, stamped 2770001 (last two numbers hard to read) and there is the number 02278. When I am looking for parts, none of these numbers match up 1979 or any other year. Am I looking in the wrong place? Thank You!