Conventional wisdom and experience is that a cast crank is good for somewhere in the 400+ HP range. I personally would not bet on the Mancini cast crank to be any particular level of quality without knowing more about it.
If you start with a 340 crank and use SCAT or Eagle I-beam rods with KB pistons, you are going to be taking a lot more weight off of the crank for balancing than if you start with a 318 or 273 crank. I don't see a crank on Mancini for under $353...??? I personally would just put the 318 cast crank in there.
