Hi Mike.
Did you know that Amel recommends (or did) using a solid coupling of the same dimensions as the Vetus flexible coupling? The engine is aligned using the solid coupling, 1/1000" tolerance. Then the solid coupling is removed and replaced with the Vetus coupling.

I had a solid coupling made at a machine shop in Puerto Rico out of aluminum.

On Kristy there is very little if any difference in vibration whether in neutral or in gear.

Hope that sheds a little more light.
Kent
SM 243
Currently Bonaire