[Blas]

It appears that you have a JAZ overflow tank. They are available in two styles; a simple tank and a reservoir/return tank. Difference being a simple tube connected to the top fitting of the overflow tank that extends to the bottom of the overflow tank. I believe the top fitting is held in place with a simple o-ring. As I recall, you can remove the top fitting and add a section of tubing inside the tank. Feel free to contact me I may have a photo. The SB expansion tank has a spacer for a tank brace that helps to support the tank from engine vibration. I have a Technical Service Tip covering the SB installation of the tank that you may find interesting. Drop me an email offline and I'll send you a copy. I'll look to see if I have anything related to BB tank installation in my reference files.
BTW: In looking at your earlier photo, the sensor tube for the water temp gauge appears dangerously close the distributor cap and wires. I would suggest that you consider carefully adjusting the routing of the coil-wrapped sensor tube away from the distributor and plug wires, and then get a short section of clear tubing (like fish tank air tubing) - slit it length wise - and put it on the sensor tube where it comes close to sparkplug wires and the cap. Why? Because one spark that would jump from a sparkplug wire to the sensor tube, could put a tiny hole in the sensor tube that will allow the gas inside to escape, rendering the temp gauge useless and your wallet a little lighter when you replace the gauge.