[RotaryWhat?]

Regarding the premix tank design---I can't think of a filler/cap location better than what you pretty much have drawn up. Attached is a picture showing the routing of the IC piping (mine will be similar)----I think your tank will still fit. Perhaps you could cut off the top part of the tank on the drivers side just to make a little more clearance? I don't think it will affect the capacity much, and if you could run the sight line out of the front instead of top I think there would be enough room. What do you think?

Also, I wanted to make sure that your tank will have clearance for the steel braided oil metering lines around the water pump---it looks pretty close in some of your pictures.