This is very confusing...
In the digital era Subal has never actually machined a bayonet into the front of the housings. A bayonet ring that accommodates the port system is attached to the front of the housing with 2 clips/four screws.
In the old days there was only one choice. Now there are more.
Subal proactively increased the port diameter to allow for fatter lenses to be installed. Nikon AF-S 105mm /2.8G VR would work in the old port mount, but it was a tight fit. 14-24 /2.8G could not fit through the port opening. The larger opening was created in response to 14-24, and with the expectation that future lenses wouldn't be getting any skinnier.
You can put an adapter on a Type 3 port (except DP-FE, DP-FE2) that allows it to be attached to a Type 4 housing. At this time there is only one Type 4 port to Type 3 housing adapter, and it is 65mm long (EXR-65/3/4). I've heard that other lengths can be made, but I've never seen it.
With D7000 a new wrinkle has been introduced. Now, in addition to bolting in a Subal Type 3 or Subal Type 4 port mount, adapters for other brand ports are planned. To my knowledge these are also not shipping yet. Adapters is a confusing term, though. This isn't an adapter in the sense of a piece that pops in to allow you to attach another piece, the user basically converts their housing bayonet to another port mount.
These housing bayonet rings could be changed in the field, but it is not how I'd want to spend my holiday between dives.
Personally, if I had a Subal port investment and was shooting DX I wouldn't go through the expense of converting to Type 4. The only lens that requires the update is 14-24, and it isn't a useful focal length on DX in my opinion.
He went from type3 to type4 so he could use the Zen dome, which only comes in type4 mount..
DP-230 is only made in S4. DP-200 and DP-100 are made in both S3 and S4 mounts.