Yes, you are right about the viper, as it can be seen in this picture it has a nice plate + PCB in the "correct" format, while the Alps Party GB has a standard 60% size unfortunately.
It would still be interesting for me if it supported the HHKB itself, even if it meant not having USB hub thought I can't promise to commit to that one right now.
A true HHKB is a whole different ballgame. Those have an integrated plate with the case. At a bare minimum you need a CNC for that. There is a reason those are so hard to produce. I'd love to try my hand at it when I do have a CNC, but I'm not sure how well it would hold up.
As for the Viper, two piece cases are tricky business (even with a CNC) you have to get everything to line up just perfect, you have to have a way to secure it, and it has to be stable - and when you take that top part of the case into consideration, things can get pretty fragile with wood. That is not to say it can't be done, but the cost would be greater than a one piece drop in case no matter how you look at it.
For the record though....I
really want to make this style of case. I think about it a lot. I'm just not sure exactly how it would come together. Oh, and if it was a "True" Viper style, as the picture you linked to showed, I would be all about getting those built. That is exactly what I want in an MX board for myself, as well.