Morphling!, could'nt you get away (spacewise) with putting a bigger outlet barb in there?, a 3/8~BSP sized barb would be excellent 5/8 AKA 16mm with a 14mm inner I/D would allow a nice pressure drop to increase impingment would'nt it?. 8mm I/D is certainly too much back pressure!, why not drill them out at least?, stainless will maintane strenght at a very thin wall thickness (it may be sharp enough to damage tubing though)...
Have you thought about epoxy/bonding 13mm Cu pipe in the top instead of threading it for barbs?, the outside profile is simular to a 1/2 barb but with much superior inner diametre...
Gorgeous block by the way
, same with the GPU block I saw last (cept I did'nt like the push fittings, minor detail!
)...
Have you really submited a Cu version to 'BAd'ams (
) for testing?, have you heard any feedback yet?...