Things to consider ... power to weight ratio - you want the most power for the least weight! Not sure how the Perkins measures up in this respect. Also needs to be high revving, so if its designed for heavy displacement boats it won't be any use in a RIB. Also can you get an outdrive to fit it? Not heard of Perkins / Outdrive combinations.
One company that might be able to give you some helpful advice is Lancing Marine in the UK. (www.lancingmarine.co.uk). They supply diesels, sterndrives etc etc.