vacuum advance

Was pulling my carb for a rebuild and wanted to ask you all for an explanation on what purpose this vacuum serves mounted underneath the distributor with a line going over to the front of the carb. Not sure what it is or what it does.

I am looking to either purchase a NOS or rebuilt distributor for my 53 willys wagon (f134) with vacuum advance (6v). Attached is a photo of one of the IGW 4189, I have two of those and 1 of the CJ style mech advance ones (someone welded the weights....). It appears as though the IGW4189 is not...