I apologize up front for the quality of the Pix, unfortunately they were a one time shot. Hopefully you will be able to get the idea.
The biggest thing I wanted to get out is the use of the Bakeable Modeling clay I used to make the dam.
Trade name "Sculpey", it works really well, a lot easier and more dependable than trying to tape up gaps.
The one Pic is of a piece of Manila folder with two cuts at either end, when folded/overlapped and taped around the handle they will give you the opening, see Pic. Then the clay is rolled out and wrapped around the two tabs, there are no end pieces the clay acts as that part of the dam. Press the clay all around, I put a screw driver in the hole when pressing over the grove to keep from flattening that area out. Pic with paper of and rough shaped.
This is a basic design, points or half moons could be added to the grove. Pencil lead rubbed in the grove will help the Pewter flow.
I use a large spoon with the bowl bent into a "V" shape to melt and pour the Pewter, using a stick to steady it like a sign painter would brace his brush.
Hope this is helpful.
Tim C.