Hi Gary and John , I have had some problems steming from a bent shaft on a factory installed 2002 Volvo engine.
I removed and replaced that Volvo with a Yanmar 3GM30F and used a Federal Flexable shaft coupling on the Aquamet 1" ss shaft.
Misalignment and bent shafts are a serious concern. On my BCC the bent shaft caused the cutless bearning shaft log to “De-Bond” from the deadwood area, and allow salt water to enter and migrate down into a damed and filled cavity in the deadwood.
I did want to remove the considerably soft Yanmar mounts, and replacing them with stiffer mounts , but was advised against that, by knowledgable shaft and prop people.
The Yanmar mounts have a different degree of shore for the forward two mounts , than the aft two mounts, and Yanmar reccomends to replace the mounts every few years, but nobody does, even me ! Also Yanmar reccomends using a flexable coupling with their soft mounts.
There is a side benefit for using a flexable coupling , in that it isolates the shaft and prop from engine grounding, through them, so prop zincs last much longer.
I have to install a fixed shaft couple on the shaft to adjust the mounts, then remove that and then install the flexable coupling, to come close, but even just attaching the exhaust hose to the water lift tank will throw out the alignment with the fixed coupling, or even leaning on the Yanmar engine will skew the go-no-go feeler gage test .
There is very little said about “Plunge Thrust” and how to compensate for that force , too , encountered when shifting fwd to reverse and back.
Hope you find something that works for you, as I did !