Will a 6 qt be enough?

Sucking a pan dry is impossible (Mopar ran tests on this back in the 70's and proved a stock pickup, even with a HV pump won't suck a pan dry) unless you run a real good aftermarket oil pickup like the kind that bolts to the pump cover. More times than not the reason for a spun bearing is from oil starvation because the stock pan has no baffles to keep the oil where it belongs under acceleration. Since you've obviously put a lot into this engine and are revving the snot out of it I'd say go for the biggest pan you can fit in the chassis. You may also want to run an accumulator for added safety.

BTW: are the rods stock? Have they had good aftermarket bolts installed and been re-sized?