Yes, the original Slim Jim clubheads are brass with tungsten plugs. You'll find the shallow clubface design is perfect when hanging the shaft vertically. When doing so, it puts the center of the clubface (sweet spot) right on the equator of the ball.
I don't think you want to buff-out that brass putterhead! It might look cool hanging on the wall, but would be terribly distracting on the golf course. What I do, and what I would recommend, would be to paint the clubhead with flat black spray paint and then paint the recessed alignment lines with some Testors enamel paint, which you could find at your local hobby store. Testors provides a huge selection of colors... *I don't paint the clubface
If you decide to have the lie-angle adjusted, the only way I've found to get this modification done properly is to drill out the clubhead and insert a sleeve. GOOD LUCK!