As for the Dungeon Loot, I am pretty sure I use the vanilla Loot Tables and inject my stuff there so MineTweaker might be your Solution, though I can add a Config to disable GT6 Loot too. 
As for the simple World hrm I never made a Dimension myself, so I dont exactly know how to do that one right, but I can tell you a few Mods that kindof add Dimensions where you can add Ores to. I think Enviromine adds one which is basically a Underground Cave with Water, Stone and Ore, similar to the nether with Lava, Netherrack and Quartz.