Someone said once that Volvo made a great diesel right up until you had to buy a spare part, and then you got an insight into the true cost of Swedish unionized labour.
At 44 feet and nearly 15 tons, you've got a pretty heavy boat. Complications like a lightweight engine or turbo would be wasted on it: you want torque, reliability and are probably indifferent to whether the engine is 600 or 900 lbs. I imagine your prop is at least 18 inches, and possibly 20.
Consequently, you might want to look at a more "tractor"-like engine, like a Kubota or a Beta, something with good access and parts you don't have to order through a "marine dealer" but from a farm machinery supplier or an auto-parts place.
You may also wish to consider the dimensions aspect: Will you have to glass in a new stern tube to accommodate a different transmission angle to the coupler? Will you have to make new engine beds? Will your favoured engine be too tall or wide for its compartment?
In my experience, these follow-on modifications can cost as much or more than the new diesel. Anticipate a few hours looking at engine drawings and measuring odd spots on your boat.
Is the Perkins completely dead? I might consider a rebuild if it wasn't, because it's got a huge user base and parts are still easily found. I might even consider putting in someone else's rebuilt Perkins if the provenance was good. I have a Westerbeke W-52, essentially a Mazda pickup diesel engine, that I'm rebuilding to avoid a lot of the hassle of repositioning everything the engine touches.