Blissboat
Guru
You keep mentioning the Range Four deries engine. I am pretty sure that engine did not come out until the mid to late 80s. The Range Four was to Perkins what the "Super Lehman" was to Lehman and they both came out about the same time. I think late 70s was a bit early for that engine. It was indeed a 6-354. But the Range Four was an updated version of that engine with a little more power NA.
Finally got around to calling Charley to catch up on a number of things, and asked again about this. He confesses that he cannot remember for sure whether it was the Range 4, although he thinks it was. He was dead certain that they started designing with the assumption it'd be powered with the 135 hp Perkins.
He ruminated about where the market subsequently went for so-called trawler-style yachts, thinking that they could have designed the West Indian for enough power to climb out of the hole and run at 12 kt. or better. I seem to recall that a few owners later turned to re-powering their W.I.s with more powerful sixes, e.g. a Yanmar and maybe a Cummins 5.9 natural.