For me I would go closed chamber and adjust with head gasket. They need a different head bolt/stud kit. Also alternator might need so fitting and depends on you exhaust. Stock 340 manifolds can hit the driver side head. Nothing insurmountable, you just buy a header flange and sandwich it between the manifold and the head. Also the valve springs on those heads are marginal for the lift they say they are good for. It you are close, with quick ramps, you might want an upgraded spring.
