Need help ~Thinking about an 1987

I am thinking about buying an 87 v20 (20.6' I think) with an omc seadrive. the current owner thinks it's a 1.8L but is not sure.
I am a bit concerned about the motor, should I be.
do they still make parts? is it a good motor? (it sounds good). what are the common problems, ( he is mixing the oil seperatly) boat itself seams in top condition.

I love the shape, size is perfect, full transon, and comes on a new-ish magic tilt. I expect that will be fine to trailer with my 99 explorer ( 5.0L v8 ).
I will be using it to fish & dive in the gulf, and don't want the motor to give up when I am far offshore.

Any thoughts. ? This will be my first boat so I am a bit in the dark here!!!