Building a Mash Tun

Last year I tried my hand at all grain brewing before I knew how involved it was. (Well, I'm still not 100% confident of all the specifics.) I had no mash tun. So I developed a half assed way of mashing and sparging involving a big blue cooler and a grain bag. It was during a time when my brewing habits were relatively slack anyway. On top of that, my record keeping was next to non-existant. So I have no idea what my efficiency or gravity was. I still made beer. A pumpkin ale with real pumpkin. And despite the fact it was way over carbonated, it tasted pretty good.
A couple weeks ago I bought one of the big 10 gallon cylindrical picnic coolers from Lowes. And yesterday I picked up the parts to convert it into a mash/lauter tun.
The homebrewtalk.com wiki makes it seem simple enough. With one exception: You must convert 4-1/2" fender washers to 5/8". It looks like it's still gonna be pretty difficult. I haven't had time to sit down and finish the job. But, at this point I'm not even sure the 5/8" hole will be big enough.
One other cause for concern: Most of the other parts are made from brass... Brass is made with lead. In John Palmer's book, he published a method of removing surface lead from brass using white vinegar an hydrogen peroxide. I suppose this will work in the meantime, but it still makes me nervous. I think eventually I'll try to find stainless steel parts to replace the brass ones.