I have been thinking about some type of rubber coupling,
Have not got any further but am interested in knowing more ?
To answer your question.
There are a number of alternatives
1/ CV. Joints
2/. Uni joints single
3/ synthetic (flexible) coupling goes between the
& the drive shaft. Main purpose
being vibration reduction
isolation of shaft
slightly reduces the criticality of engine
4/ Manufactured solutions
Try also vetus
Start googling it. NOT CHEAP
possibly as much as . $3000 + & more
All have there pros & cons
I have no experience of any
Except the flexible coupling !
Engine alignment is still an issue for me
To truly disconnect engine alignment from shaft alignment,you need to
Have a double CV or uni joint.
This can also have issues unless set it up correctly
The only other alternative I can think of is to use HYDRAULIC or electrical