Concerning using graphite vs. steel as a sacrificial anode, I noticed that many who do electrolysis preferred to use graphite rather than steel, so that's what I started with.

But since big parts of sheet metal that need cleaning, such as a dash frame, have a lot of area, likewise the anode needs a lot of area too. It may turn out that I'll like using scrap steel sheet for anodes with a lot of area better than graphite with not so much area.

Concerning the use of bolts and rebar as anodes, these have only enough area to treat small parts efficiently.

"They (anodes) should present a large surface area relative to that of the piece being cleaned and be able to 'see' most of the surface of the piece from all around to minimize areas of non-cleaning due to shadowing effects, as the current in the electrolyte tends to travel in direct lines rather than around corners. An anode made from a small piece of steel rod, for example, will work to a degree, but is less than satisfactory....An alternative (to completely surrounding the part on all sides, top, and bottom with anode material) would be to simply turn the piece part way through the process to make sure any surfaces which had suffered shadowing effects are treated."

from http://myweb.tiscali.co.uk/andyspatch/rust.htm

Concerning current in the electrolyte tending to travel in direct or straight lines rather than around corners, this is more acute when using a small container such as a 5-gallon bucket. When using a container as big as a wading pool, this effect is less pronounced. My dash frame did in fact get some cleaning on the side facing the bottom of the pool and not facing the anodes. On the other hand, at the 4 big bolt holes for fastening my K frame to my unit body, there are pockets, one shown in the photo, that were "shadowed". I will need to redo those K frame pockets with a special setup - anodes that stick into the shadowed areas.