Shaun, very interesting that you bring this up. One year ago we determined that we needed to replace the cutless bearings on our 1988 single engine engine (CAT 3208NA) 36' GB Classic. Knowing I was not going to do this in my driveway I was, finally able to find a yard that would do it. (After contacting 15). Originally the yard was going to only replace the lower...I mentioned the upper would have similar wear and should be replaced. In the mean time, I contacted the previous owner who told me that he thought there were 3 bearings that he replaced in 2007. I mentioned that to the yard, they said no and the GB drawing I had, showed only two (circa 1974). My shaft is 2" x 17' so I thought it plausible to have 3 but I went along with the boatyard to replace two.
While removing the shaft to replace the 2 cutless bearings, the shaft tube came out with it. The boat yard notified me and told me that that shouldn't have happened but will be no problem. I asked if that was caused by an unknown third cutless. They said no.
When all was said and done, I received 2 new cutless bearings, stern tube/shaft tube was reinstalled and re-bedded, New shaft seal, Rudder repacked and new engine mounts to enable proper alignment. (My suggestion)
Based on the length of my shaft (17') the amount of shaft ahead of shaft seal to tranny and the tail beyond the lower cutless, there would be about 11' of shaft (2") between cutless bearings which while running is very smooth, no vibrations....so I conclude and along with what I see in the old GB Drive train drawing that 2 bearings are correct. My shaft tube was one piece, composite.
Sorry for the long story, but funny that the 3rd bearing scenario would come up again.
Good luck
Mike Dana
Third Reef
36' Grand Banks Classic #819
Potts Harbor, Maine (South Harpswell)