Bulb depends on the make and model of the light fixture.
My 1982 8.5 has a Perko model 1331 steaming light.
I replaced it several years ago with the smae model, however the bulb was different. So you may have to check the fixture to see what style bulb it uses.
Current Perko 1331 light uses a 31 mm festoon bulb (double pointy ends, just like in the buttons style, deck mounted navigation loights.