Hmm, the John Deere engined Pacific is 115 hp and belonged to Del Connelly, Portland Diving School. although less power he thought it went faster than the original Mermaid engine because it was lighter, however I think that the wear on the original engine might have had something to do with it.
Since the engine is fitted with a jack shaft it should be possible to install anything in that huge engine box afterall someone put a V6 outboard into a 7 series BMW in Aus for a giggle.
The new RIBs are powered by Cummins 4 BTA marine diesel engines rated at 150 bhp @ 2800 rpm coupled to a Sternpower leg providing a service speed of 22 knots.
y the way the 101 stern drive model has a recommended max touque of 350 ft lbs which is about 175 hp.
Having said all that best keep it simple and there are lots of Ford Mermaid engines about.