Have you had a chance to test out Bobby Grace's M3 putter. It is center shafted and seems to have two weights at either end.
http://www.macgregorgolf.com/products/product_display.aspx?pid=14
I was using his "Fat Lady Swings" Mallet for a while and have now gone to a Plop blade. I seem to get beter feel for distance with the blade.