I have a 1986 catalina 36 that was repowered 2 years ago with a 25xpb.  I am considering replacing the hurth zf10 transmission with a twindisk 340mg.  The twindisc tranny  is about 3/4 " shorter then the hurth.  I only have 3/4" between the strut and face of the prop.  I am thinking I can use a flexible coupling to work as a spacer and driver saver and gain the need length to accomidate the twindisc.

The reason I am replacing the tranny is because every time I change the tranny fluid it is opaque in color with a billion fine gold metal flakes.  Yes I sail with the tranny in reverse.  It was installed and adjusted by a universal dealer in Seattle.  The tranny is currently working. The unit has a brand new prop since install from catalina direct michigan style 15x10.  The tranny also has the extra heat sink water cooler attached.  I change the oil with redline syn every 20 hours.

Who uses the flexible couplings, recommendations?