ive seen a couple of rover v8's in jetboats but dont know who marinised them.maybe worth getting hold of sam at west end marine who made striker jet boats,he tried lots of different engines, maybe he can help.
Hi mi old man http://www.lancingmarine.com/ has done lots of Rover V8s were popular with ski boats at one time plus jet pump combos. Used Nixon cast Ally (Log) Manifilds & Risers + Indirect or Direct cooling.
Thought I would add this url http://www.rpiv8.com/homepage.htm for RPi for some serious Rover V8 performance & tuning - have used for mi old TVR now sadly languishing in mi garage.