I think the taller tank would be perfect at the engine guard height.
Here is the diagram for mine. I forgot the gentlemen's name, but he wrote up a great explanation for the header tank system and also posted on the GT40 sites. I'm sure you can do a search on this site and read the details.
I'm using a FlowKooler water pump, so it has an extra port to connect to the bottom of the taller tank.