I was able to adjust the lower shift cable stud to the furthest rear (aft) of the boat. I wasnt getting enough tension on the cable to stay engaged in reverse.
I will do an in water test to verify the problem is gone.
I have a 70s model mercruiser 470 mc-1.
It will not shift into reverse with the upper cable attached.
But it will shift fine when I disconnect the upper cable and move the shift arm manually.
The boat did shift when I bought it. I replaced the bellows as well as the lower shift cable...