Stress relieve is an exact science requiring precise temp control.If you harden it the machinist will not like you. Flame cut shops send stuff out for stress everyday, in our case it would add 2 days to the lead time but I dont believe it would be required.It may benefit by easing off on the hardness of the flame cut edges but still again they are readily machinable without stress, anneal etc. Rifle barrels are now being stressed cryogenically ! Old time machine tool builders would place the huge machine castings out in a field to reside for a few years of freezing/warming to normalize them prior to machining.