You could just make one that will attach to a 3 piece SS ball valve and have it extend about 5" to the left (facing the valve from the outside). On my 10 gallon BoilerMaker kettle, the sight tube starts about 5/8" lower than the ball valve underside (just under 1.5" from ground level on the sight tube, about 2.07" to the lowest part of the valve housing/assembly). You could put a small piece of metal to keep the spacing under the sight tube housing.
I'm planning on gluing some carbon fiber welders blanket (1800F tolerant) to the top side of the heat shield that came with my BoilerMaker kettle. You might want to do the same to the up side of your item. I'll be using glue that's good up to 2300F to do this. All from McMaster-Carr.