I believe he is referring to what most call "cinder blocks". It is 12X6X8" fired porous concrete block ... usually with two large holes through them. I have built many BBQ grills and other high temp things from them, and they seemed OK. As with the red clay construction bricks, there needs to be a good layer of fireclay or refractory covering them where they are exposed to direct high heat. The hollows could be filled with dry sand, or left open to provide air insulation.. They certainly would work for the hood back/bellows wall instead of adobe.
Check with your refractory supplier and see what he would want to ship a small batch of firebricks ( about 10-15) along with several sacks of Cast-o-lite 30 or similar refractory ( Satanite mixed with sand would work, but the castable refractories are better). Cast-o-lite 30 or Mizzou would make a very good firepan that would last almost forever. They line crematoriums with it.
If only satanite is available, you could make a 75% satanite - 25% sand refractory mix, or use pure satanite.
I would guess you will need 30 to 50 firebricks for your forge to do it in the traditional fashion, depending on the brick size, your design, and forge size. You want hard firebrick, BTW, if that is route you go. They are the same kind they use for lining boilers, chimneys, and fireplaces. They cost about $5 US each, and are available here in hardware stores and lumber yards. If you don't build it with firebrick, you still want at least ten hard firebricks to use to temporarily alter the forge trough length and width as needed.
A much cheaper alternative to hard firebricks would be the red clay cored bricks ( the ones with three holes). While not intended for direct high temperature exposure, they will do fine with at least 3/4" of refractory over them. People have been building bread and pizza ovens, smokestacks, and fireplaces from them for centuries. They just need a refractory lining. In the hottest areas, like the floor and tuyere areas, use 1" of refractory. They are available at any lumber yard or building supply. Use ones would be fine. New ones cost less than a buck each (currently, 50-60 cents each US). Use satanite to mortar them together.
A tip is to have the forge trough about 1" narrower than your firebrick length to allow setting firebricks over the trough to make an "oven" for HT. Standard firebrick size is 9"X4.5", so an 8" wide trough or narrower is good.
If firebricks just are not going to be available, you can cast your own in an oiled wooden mold from 50% satanite - 50% sand, or from castable refractory like Mozzou/cast-o-lite 30/etc. This wouldn't be a good plan for a whole forge, but would provide the ten or so bricks needed to alter the forge for different configurations and projects.
In the old days, we used to mix asbestos powder with a satanite like refractory cement to make a high temp and strong refractory. It was a common industrial procedure, and came either pre-mixed ( just add water) or in separate powder containers to mix your own ratio. We often mixed it by hand to the desired consistency and applied it barehanded.
Two folks that I knew (one I worked with) have died from mesothelioma. I have been checked and am fine. I did not mix it that often, although I worked with many asbestos items back in the 60's and 70's. Asbestos paper was used to line casting flasks, and a big woven asbestos blanket was used when welding to prevent fires. Soldering pads and boards were made from rolls of asbestos paper. Asbestos gauntlets were used to take things from burnout ovens and HT kilns. I still have a set of the huge asbestos mittens used by steel mill workers on the shop wall .... encased in a double layer of plastic. In those days asbestos was considered the perfect insulator and high temp refractory. Even the siding and roof shingles on houses were made from asbestos.
You could buy shredded asbestos in 5 gallon barrels at the welders supply. You mixed it with water to make a temporary heat shield when soldering and welding, or with a cement to make a refractory, etc. In those days, you rarely ever saw a respirator used.
Needless to say, I don't do any of that anymore.
