I saw a picture where the builder used a radiator cap that was mounted in line with the top radiator hose next to the thermostat housing.

It looked like tee with a radiator cap on the top.

I'm using the stock radiator out of my 1979 Chev.
Mounting it behind my lower grille. I need something like what I saw in the pic so I can access the cap, because the cap on my radiator will be innaccessible.

I need to know what that item is called and if anyone knows where to get one, it would be appreciated.