Building a Gas Forge

Hi All,
I have an ambitious build planned and I could use some advice on building two forced air natural gas forges. I have a 3/4 " LNG line already in shop, but it feeds the home furnace. Standard volume, water column for residential. A plumber friend suggested running a bigger line directly from meter, so not starving out the furnace and killing the pilot in winter. Not cheap, but will do it if it will work. I just don’t want to deal with the propane tank refills if I can help it. A PIA around here unless you want to get exchange tanks, pay premium for roughly 3.5 gallons of LPG.

I’m going to be using 2" thick ceramic hardboard, kaowool blanket fill and 1/8" thick steel rectangular boxes I had broke up. Forge brick on bottom of boxes with hardboard top and sides. All this will reside inside two sections of what used to be an offset barrel smoker, two separate forges, one for heat treat or long stock ( 34" or so) and a shorter one that used to be the smoker firebox, about 16" long. Diameter of both cylinders about 16" or so. Effectively, will be rectangles inside cylinders with insulation all around, and brick in the actual forge space, I’m filling the space between the “boxes” and the outer cylindrical shell w/ kaowool.
I reasoned that I will get less btu’s w/ LNG than propane, so had to adjust for that.

As a result, they will be highly insulated, with doors at each end to keep heat in/or not at will. Forced air added via a Dayton blower motor or two, and a slough of plumbing parts to mix the fuel w/ air, effectively a carburetor. I have no idea how to construct the nozzles though. I’m thinking mig tips? What size might work with LNG? I’m going to fabricate cones from castable material to place the actual nozzles into the firebox. Working space in each forge will be about 9" wide and 7" high.
I know it will be a trick adjusting the fuel/air mix, so have valves to adjust air up/down. Using large diameter pipe for air side, like 2" w/ gate valves , necked down with tee to mix fuel in.
Anybody have any experience w/ this? I will post some pics of the main components.

Hey @63steward - I just noticed this snuck into an announcement so I moved it into it’s own area. How did your build finish out?