Hi Gwertheim.
I'm not necessarily going to be building production versions of this case. At present I am building a prototype for Dice and I'm not set up for production.
QC process depends on production volume. If these parts get tooled then there will need to be a first article inspection to the drawings. This is normally a statistical process check on all the dimensions. After that you can ask for 100% inspection on some critical dimensions on the production line. Quite often this can be accomplished by making a set of go no go gauges for the production line.
The other thing to make sure that the part datums are thought through so that everything ends up square and you keep the tolerances as tight as possible.
Finally the distributor plate is probably going to be the most critical functional part. I would expect that it will need a 100% leak test. Probably using air under pressure over a period of time.
I'll be happy to help Dice as he gets into these issues.
Thanks for that detailed answer, was exactly what I was looking for