The present application thus describes a method of manufacture for a late lean injection system in a combustor of a combustion turbine engine. The method may include the steps of: a) identifying a desired position within the flow assembly for a late lean injector, wherein the late lean injector comprises a late lean nozzle and a transfer tube; b) corresponding to the desired position for the late lean injector, identifying an injection point on the inner radial wall and a late lean nozzle position on the outer radial wall; c) positioning the inner radial wall and the outer radial wall in an unassembled position; d) while in the unassembled position, forming a hole through the inner radial wall at the injection point and slideably engaging the transfer tube within the hole; e) installing the late lean nozzle in the outer radial wall at the late lean nozzle position; f) positioning the inner radial wall and the outer radial wall in an assembled position; and g) connecting the transfer tube to the late lean nozzle.