Scott,
That is a rather dandy piece that Randall Thomas at Performance Unlimited makes for Superformance Cobras.
It is a 2 quart overflow (and most importantly) and recovery tank for the radiator.
http://performanceunlimited.com/cobr...thertanks.html
Most installers give you a Jaz tank mounted low, which is most useless (IMHO) since it does not allow recovery of any coolant. This unit allows for the cooling system to pull the overflow back into the system rather than burping it out all over the engine compartment, or you have to manually drain it.
They are really nice.
E