After conversing with my friend and expert brass worker Jeff Kraker, I dove into changing the tender. He suggested that I use brass wire for the tender wrap over. I had fairly good success with using his technique on the first try. One end did get bent a little while I was working with it, which made things more difficult than they needed to be. I cut the old top off using a dremel tool cutting disc, then filed to get a flat surface on all three sides. Not a perfect fit but close enough, especially for the first try. The new brass top was mounted onto the tender shell using AC glue.
Here's one of their shays: http://www.gearedsteam.com/shay/images/kelley_island_lime_n_transport_co_17-sn793.jpg