Oil overflow?

Hello,

I've got a rabbit race car that I'm putting back on the track. I've run it a few times, but I'm going racing this weekend at the ridge, and it struck me that I don't know how much oil it takes...

Ive been putting 4.5 quarts in it, and it has good oil pressure and temps. 

it's got this big over flow, with a gauge of sorts on it. Is this for extra oil capacity? It's the aluminum rectangle with the blue hose going to it.
 

i

That just looks like a really nice catch can to me. I had a Rabbit I auto crossed that had 13:1 compression, I had a big catch can on it attached to the same breather. That bump in the cover is an oil separator, it doesn't do a very good job sorting the oil from the air.