But you see a lot more old OMC motors,----OMC used stainless shafts around 1950.---Mercury switched 25 years later.------No special tools or shimming required on those " stupid gearboxes " either.
The lower shift rod screws in all the way.----Then backed out so that it " leans " forward.----Line up the notch in the coupler BEFORE you put the bolt in.----Done.
Those cowlings alone are " hefty " in my opinion.------Got one of those for free last fall at a dealer.-----Only thing to do on those is a complete teardown !
???----The plastic drive keys / bits last for 20 years or more.----Your motor is " special " I guess.----And perhaps your motor does not have a 1982 lower unit.----And there may have been 2 different plastic keys.----Some " club fisted " person installed the wrong one ?