The 75 was made from 75-84
1980 they went to a 1 piece lower unit.
Pics of the gear case and the electronics will help.
Under the bottom carb on the intake is a foundry stamp.
If It says 79 in the center that was the year it was made.
Not the year it was used. I had an 88 that was made in 87 and sold in 88.
To add pics you need to use a photo sharing site, something like shutterfly ETC.
Just 3 posts?? I thought it was 5?? Learned something new.