Well... I really like my shiney upgraded Aquamaster, and I'm not convinced that performance wise the Kraken is a lot better. Functionally they're pretty much the same thing.
I also used to like shiny a lot. Actually, I still due, but like everything in life... I had to make decisions based on the trade-offs. The early Argonaut testing were all done using vintage metal cans. They are mostly interchangeable by design. At one time I did consider continue to use the metal cans (on my own personal regulator) even after I designed the plastic cans.
The plastic cans do have two advantages. The first obvious one is the weight. I can't remember the exact difference in weight, but it is noticeable when you are holding the regulator. The difference in your luggage didn't bother me as much as just how it felt.
The plastic can also has a much better horn air flow profile. I can tune the venturi flow much better with the plastic cans. The flip side is that to get that much venturi flow, then you have to use the DSV mouthpiece with the flow diverter. There are no disadvantages to doing that, but some divers like the looks of the vintage curved mouthpiece. It used to be my favorite mouthpiece. I will say, that once I got it all working together, I have not looked back. I have several beautiful Phoenix-HPR that have not been wet in years.
The horn in the metal cans were fabricated with a rectangular attachment to the can due to the fabrication process and the difficulty of creating a complex transition with the metal parts. If you notice the circle of the horn is bigger than the curved surface on the side of the cans. Fabrication limitations (by stamping, forming, and joining by brazing or soldering) were major considerations when designing the vintage cans.
The Phoenix to main body joint:
When I was playing with the installation of the Phoenix I played with several different sealing methods. I used both types of gaskets and also tried several other washers and hard O-rings from McMaster Carr. It was always a trick to get the rotation just right for the "perfect" port location. In general I would also tend to torque the Phoenix probably a lot higher than most people would be comfortable tighten it. I never caused any damage, but I am not recommending that.
The one thing I meant to try, but I never got around to it (before the Argonaut project started) was the use of sealing Loctite on the threads. There is a large variety of Loctite that are design to to seal. I would not be at all afraid of any toxic possibilities since I would still use the gasket. There are two basic families of Loctites. One is considered semi permanent and can only be unscrewed with the use of heat. The other type is also very secured, but it can be taken apart much easier. I would consider either one, but I would probably start by trying the second type.
Installing the Phoenix as a mostly permanent installation is reasonable. You can service the regulator without ever disturbing the joint between the Phoenix and the main body. Lets say that I have even considered soldering the two together as one unit.
Again, I have not tried the Loctite myself for this particular application, but that was my next step. Like I said, I haven't touched a Phoenix in like 7 years.
BTW, there are several other advantages of the Argonaut over the Phoenix-HPR. If you do a search at VDH you will see some of my early write-ups about all the thoughts that went into designing the Argonaut. Yes, they mechanically share many of the same parts, by design. That was very intentional for compatibility and long term parts availability, but there is more to the design.
The one thing that both of these regulators share in common is the long term parts availability. The reason they share most of the internal replaceable parts is that I was trying to use parts that should be available when your kids and grand kids decide to take up diving.
You will have to protect the silicone rubber parts (the hoses and the large diaphragm), but the mechanical wear parts should be available as long as Aqua Lung, Mares, or Trident are still in business. All three have seats that are compatible.