Curtis, your work always impresses me - clean, neat, artistic and workmanlike.
A little late, but:
Next time you are out of SILVER silver solder, holler! I almost always have some on hand. Mostly I use the paste version of lowest temp stuff, but I do have a couple pennyweights of medium, and a bit of hard.
Checkering - Did a lot on cartridge-type firearms, pistols and rifles. But all VEE-type, not flat-topped. We will have to trade techniques some time. I have used both thin aluminum and plastic for keeping that first line straight. Just a thin strip of either, about 1/4" wide. Generally I cut up plastic dividers as used in 3-ring binders. Makes great patterns also. When you are laying out your checkering pattern, the clear lets you see the grain where you will be cutting. I've made a couple patterns for the Lehigh, tang and forestock. easy to take small pieces of tape to stick them on and draw around the outline.
At any rate, the firearm that you are working on is simply beautiful! Hope the checkering goes OK.