The old water in the baggie trick.
Works well to determine total volume, and minimum and maximum fluid levels.
Tried several different shapes and sizes for the coolant recovery tank. The limited space makes it impossible to do what I want.
For now, the best option is to go with this size and shape. Will need to cut down one corner and weld in a triangle, to make clearance for the radiator hose.
The overflow hose fitting is another problem. More on that, later.
Trying to design a sight window. Wanted to center a window in one triangle opening in the frame, but the window was too small.
Working on a full-size window. Trying to design the corner radii, and clearance for the o-ring and bolts. Hope things work out okay.