Plumbing in the Home/Pop up assembly
My bathroom sink dates from the 40's. I had it resurfaced and put in a new pop up. The lip of the drain is too narrow and there is an ugly ring...can I buy a brass pop up with a wider lip...it is a brass/gold finish
The pop assembly is an industry standardized dimension. By that I mean the hole in the sink basin has to be the same for all sinks in a particular category. (kitchen, bathroom, bar sinks ect...) The flange for the pop up can vary slightly but usually a manufacturer will not vary to much so his product will work in 99% of the basins out there. There are pop ups available in a multitude of finishes and again, some are slightly larger. I would measure what you want to cover and go to the local Home Depot of plumbing supply store and to to find one that will do the job. I have noticed that it doesn't matter what the pop up is made of, it usually varies with a particular design or series.
On an other note if the ring you are referring to is a rust rind, try using a product like "iron out: or "C-R-L" to remove it