I'd say for a huge drum you need more than 12V, I have used a 28V power supply from the aviation industry with good results. Or two 12V batteries in series...
To get as close as possible to the anode I have often put the parts to be cleaned in a container and sat it straight on the anode.
I too have reversed the anodes - I've also used this process to age metal when I was making reproduction hinges
Well, after only 2 hours of running I have given up. The knock is terminal and I think any longer it will give up and cause a lot of damage.
So its been retired briefly and the 16hp out of a C-161 is in its place.
Not as straight a swap as I hoped, the starter is lower down. The oil drain is different, and the wiring needs changing to add 12v to the coil...