Having had a quick look, it appears to be a reasonable design. You might have to do a lot of searching to find cylinders that size but if you have the patience and the determination you'll get there.
There is a an online calculator for firebox size, chimney size etc somewhere (found easily on Google) that will help you in tweaking plans to fit whatever parts you can find.
Alternatively if you don't need portability, search for double barrel smoker, this design works well and is made from two oil drums which are easy to find.
Also I've got plans for a Backwoods clone I can give you. This design is great and cooks really well although it is fairly expensive to build.