Skeet, the narrower the V6, the easier the swap will be into the 544 engine bay. There are 60 degree V-angle engines out there, and at least a couple might come with an overdrive automatic.
That said, I'm curious to know why you want to repower the car. Is it to be a daily driver and you need the high speed cruising ability? Or do you want to build it into a performance car/streetrod?
The 544 is a great car. some call it an old-school sports sedan. It drives like nothing else, has a sound all its own, and a particular feel to its controls. The engine and transmission have a lot to do with the 544's character. Free expression and creativity are great things. So is driving a car that gives you a unique experience.FWIW.