Step 5: Different ways to make the GEK
For the obtainium route, you will need scrap tanks of 10", 12" and 14.75" diameters. 10" is typical for hand held air transfer tanks and some truck pony tanks. 12" is typical for 5 and 10 gal propane tanks. 14.75" is typical for a 100lb/25gal propane tank. (Warning: There's a surprising amount dimensional variation on "standardized tanks" between different tank manufacturers. This can complicate the fit of flanges and end plates to the scrap tanks.)
The more elegant way to build the GEK is from purposed cut and rolled sheetmetal. Sheet metal is still very inexpensive, and you will have better dimensional control than via the obtainium route.
You can cut the sheetmetal to make the vessel tubes, flanges and end plates, using a gas torch or plasma cutter. Potentially even a sawzall, but ugh! Ideally, the tool for the task is CNC plasma cutter, which can run off the CAD files provided here. Many "manufacturing on demand" providers offer cnc plasma cutting services, so you could order in perfectly cut sheet metal to get you started, and not spend all your enthusiasm fighting the prep work. ALL Power Labs can also provide readymade sheet metal and plumbing kits. See here for more information about readymade GEK wood gas kits.
Hopefully one of the above scenarios will find a good match with your abilities, time and money available. Whichever route you choose to build the GEK, the final unit is the same, and thus experiments and customizations are easily sharable across the GEK user community.