Re: Shift rod swap
No, the first three years of the V6's ('76 - '78) were different (I found this by researching the parts diagrams at brp.com). This one will not unscrew (at least from the parts diagram it doesn't look like it's supposed to, and a reasonable amount of force hasn't budged it).
By the way, what brought all this up is that I bought a lower unit on ebay which was advertised as an '89. When I got it I found out it was a left hand gearcase, as well as having the different shift rod configuration. Looks like my best bet of recovering some of my loss is to resell it (and be honest about which engine models it will work on). I'd like to be able to put the newer shift rod in so that it would be useable by a larger range of engines, but I'm doubting if that's possible.