An assembly able to be positioned in a stomach to define a sleeve receiving food and a bypass portion, the assembly comprising: a bougie configured to enter the stomach, the bougie comprising: an elongated body having a segment being shaped to follow a lesser curve of the stomach, and an extension member having a proximal portion connected to the segment of the elongate body, the extension member being movable from a retracted position in which the extension member is generally aligned with the elongate body, to an extended position in which the extension member extends at an angle away from the segment within the stomach for positioning a distal portion of the extension member away from a gastroesophageal junction of the stomach; and a sheath comprising a tubular body having an elongated main lumen in which the bougie is inserted, the sheath being translatable along the bougie between: a first position in which the tubular body at least covers the extension member of the bougie for maintaining the extension member in the retracted position, and a second position in which the tubular body is staggered with respect to the extension member for allowing the extension member to move from the retracted position into the extended position. a bougie configured to enter the stomach, the bougie comprising: an elongated body having a segment being shaped to follow a lesser curve of the stomach, and an extension member having a proximal portion connected to the segment of the elongate body, the extension member being movable from a retracted position in which the extension member is generally aligned with the elongate body, to an extended position in which the extension member extends at an angle away from the segment within the stomach for positioning a distal portion of the extension member away from a gastroesophageal junction of the stomach; and an elongated body having a segment being shaped to follow a lesser curve of the stomach, and an extension member having a proximal portion connected to the segment of the elongate body, the extension member being movable from a retracted position in which the extension member is generally aligned with the elongate body, to an extended position in which the extension member extends at an angle away from the segment within the stomach for positioning a distal portion of the extension member away from a gastroesophageal junction of the stomach; and a sheath comprising a tubular body having an elongated main lumen in which the bougie is inserted, the sheath being translatable along the bougie between: a first position in which the tubular body at least covers the extension member of the bougie for maintaining the extension member in the retracted position, and a second position in which the tubular body is staggered with respect to the extension member for allowing the extension member to move from the retracted position into the extended position. a first position in which the tubular body at least covers the extension member of the bougie for maintaining the extension member in the retracted position, and a second position in which the tubular body is staggered with respect to the extension member for allowing the extension member to move from the retracted position into the extended position.