I too believe that both of the viewfinders come out of the same factory. I own a Sealux CD70 and my review of the housing was posted on this site recently. ( http://www.wetpixel.com/module-pagesetter-...-3-pid-46.phtml )
When I posed the question to someone who had queried Subal on this point they informed me that Subal's response was that their viewfinders were produced by the same manufacturer that made their ports.
From pricing on Sealux's website the difference between the CD70 with and without viewfinder is 474 Euros; that's about US$602 for the Sealux viewfinder.
Sealux also informed me that it would be possible for them to transfer the viewfinder to another housing in the future (one of their's obviously) if the original houing is sent back to them. I posed the scenario to them when discussing upgrades to future housings for yet to be released DSLRs.
The viewfinder itself is fitted to the housing in much the same way as any other port. It is an independent component and has a thread which screws through the housing wall and is secured on the inside by a circular nut. I suspect that with the correct spanner it is about as easy to install as a strobe port.
Colin