...is run the Fennin Ro script that starts with Guardian of Doomfire. Go through and kill the demons with the dudes until you reach the end. Once you kill Omni Magus Crato and Warlord Prollaz, Fennin will pop along with 6 elite guardians of ro in the front and 4 in his chamber. Fennin will stay up for 4 hours, but the elite guardians will respawn every 5-6 minutes or so.
So just leave Fennin alone and kill the elites. As a 105 mage, Fennin never aggroed as long as I pulled the two closest elites with a non-damage spell. Drop rate on the guts is probably 1 in 2.5 elites so every cycle, you should get about 4 fiend guts. I just did it and got 150 guts during one Fennin spawn, not trying very hard to kill as fast as possible. The staffs also drop from the elites so it's pretty much one stop shopping except the molten ore.
Edited, Aug 6th 2018 7:31pm by Brickhaus