Archangel has a great design and will pack a huge punch. You might want to reconsider the weapon motor though; the 5020 is meant to run at 12S and on a 6S pack, its only going to produce 942 watts (1/4 power) and top no-load speed with a 1.5:1 reduction of 6,600 rpm. You will need to go to about a 10S, 37V pack to realistically get the bar spinning at the speed you want, or find a motor with at least an 850KV rating to stay with 6S packs.

Without knowing the weight and MOI of the bar its hard to work out the power rating of the motor needed to run it. Some of the best high KV motors I found are the Scorpion HKIII-4025-890KV Motor and the Hacker A50-8S Turnado V3 Motor - they may have the power & torque to spin that bar up with a 2:1 reduction.

I think the smartest thing is to use two 5S packs with a bit lower AH rating and then do split voltage wiring like I did in Mr Mangle. that will give you 5S to keep the 775 motors happy and 10S for the 5020 Scorpion motor. You could go with completely separate packs for the weapon & motor, but its likely to weigh more.