I've heard the 390's are hard to dial in. Also need to have power check valves/ I have two 600 polished cfm edelbrock carbs sitting on a offy intake but way to much carbs for my engine. I think even the 500 edelbrock would be to much although I've run a couple 3 duece set up which push me back into my seat when I open them all up. Love the looks of the dual 4 barrel's and the sound is to much