If it was me I'd sell the 340 to some one who desperately needed one and then use the money to build the 360. Twenty more cubic inches means twenty more HP.
I never got that one, true a larger engine can make more power at any given rpm but given similarly built engines wouldn't the 340 would just make it at slightly higher rpm?
Since you already picked your gear the largest engine will work best. The cheapest would be a 360 or a 3.58" stroked 340.