cast crank to forged in 440

Cast cranks are fine as long as they pass a magnaflux and straightness test.
Debur them and with some good quality machining and a proper balancing job, they should easily withstand 500 to 600 h.p. as long as you don't rev them to the moon.
As you want to run a 4 speed, get the pilot hole machined to accept a pilot bushing and have it installed and reamed to size.
It shouldn't cost too much extra if you are getting all of your work done at the same place...........