Gear box fluid, transmission nuts and bolts at the coupler, engine bolts where they fit to the angle iron frame and the engine mounts themselves,all need checked.
The G5 prop is not normal for a Super Maramu and it needs serviced more regularly than the H6.
Brompton told me this only two months ago.
The worst vibrations that I ever experienced turned out to be a sized gearbox due to the transmission heat exchanger failing and dumping the fluid, but the vibrations occurred only when the gearbox was engaged with the engine running.
It is really important to find out when the 110 hp Yanmar was fitted did they retain/install a shaft brake which will rule the prop in or out.
Sorry this reply is a bit tardy but anyone of the above could be part of your problem.
Seafever of Cuan