Water cooling block for multiple boards

I am going to make a single water cooling block to cool either 30 Burnin or 38 Klondike K16 boards.
The strategy is to keep it simple KISS and use off the shelf parts. This is not built yet so any suggestions welcome.

The preliminary plans and CAD drawings below is for a 10 x Burnin board water block (for 30 board size it will be 3 x the length)
 
BOM:
Aluminum rectangular tube 200mm x 50mm x 600mm x wall thickness 3mm
Aluminum flat bar (x2) 160mm x 560mm x 3mm
Aluminum flat bar (x2) 50mm x 200mm x 3mm
Aluminum weld in hose fitting (x2) TBA
Heat sink compound TBA
Heat transfer insulator TBA
Aluminum mesh 10-20mm mesh size.

Welding
End plates fully welded both ends of rectangular tube to make waterproof and then pressure tested - TIG weld.
Heat sink plates to be tack welded in place on both sides of rectangular tube - TIG weld

Heat sink materials
The plan is to put a heat sink compound between the pre-drilled and tapped heat sink plate and aluminum sq tube.
Heat transfer insulator material TIM between the plate and the boards. At this stage I have no idea what i am going to use and any suggestions would be welcome.

CAD files
I will post the CAD files when complete.

Notes:
This is a consolidation of discussions in threads here and here.
Mesh will be stuffed into the aluminum sq tube to increase surface area and create turbulence.

Concept drawing

Heat sink plate render - fit Burning board

Heat sink plate CAD

Aluminum tube render

End plate render