Abstract: Rapeseed is one of the most significant oil crops globally, and mechanization is critical for its efficient harvesting. Swath harvesting, a method that involves cutting the crop and leaving it in windrows to dry before threshing, is widely favored for mitigating the issues of inconsistent maturity and high pod shattering losses associated with direct combining. However, existing rapeseed swathing equipment faces significant technical bottlenecks that hinder operational efficiency and agronomic quality. Specifically, conventional headers utilizing side delivery modes often suffer from poor uniformity, resulting in disordered windrows and stalk entanglement. Conversely, headers designed for center delivery frequently produce dense, rope-like windrows that are ill-suited for the rapid drying of high-yield, high-biomass plant varieties, leading to potential mildew and grain quality degradation due to poor internal ventilation. Furthermore, the prevailing market solution relies on dedicated headers for either side or center delivery, forcing farmers to invest in multiple specific attachments, thereby increasing machinery costs and reducing field adaptability. To address these distinct practical challenges and improve the adaptability of harvesting machinery, this study proposes and develops a novel, adjustable delivery header based on a modular design concept. The core innovation of this system lies in its ability to integrate both side delivery and center delivery functions within a single unit. This integration is achieved through a transformable conveying module that allows for the precise adjustment of the spatial position of the delivery mechanism. Consequently, the header can realize on-demand switching between the two delivery modes, enabling operators to adapt to varying field conditions and crop densities without replacing the entire header assembly. To ensure the scientific rigor of the design, a comprehensive kinematic analysis was conducted. This study investigated the complex motion of rapeseed plants during the cutting, conveying, and laying stages under both operational modes. By analyzing the velocity vectors and trajectory equations of the stalks, the research revealed the intrinsic mapping mechanism between key operating parameters and the final windrow morphology. Additionally, the theoretical model was refined by incorporating strict boundary constraints derived from the agronomic requirements of rapeseed swath harvesting, such as minimizing impact force to reduce seed loss and ensuring optimal stubble height for windrow support. Validating the theoretical framework involved a rigorous experimental approach. A quadratic regression orthogonal rotation combination experiment was designed to quantify the interaction effects of critical variables. Through multi-objective optimization analysis, the study sought to balance competing goals such as maximizing uniformity while minimizing structural complexity. The optimization process yielded a precise combination of operational parameters: a reel speed of 32 r/min, a conveyor belt linear speed of 2 m/s, a forward speed of 0.8 m/s, and a conveyor belt inclination angle of 29°. Field verification trials were subsequently conducted to evaluate the performance of the prototype under real-world agricultural conditions. The quantitative results demonstrated superior performance metrics. The average laying angle of the stalks was recorded at 14.5°, a critical parameter that facilitates optimal airflow through the windrow. The consistency of the operation was highlighted by the minimal difference of only 3.7° between the average angles of the upper and lower stalk layers, indicating a highly uniform structure. Furthermore, the average laying width and thickness were measured at 1128.4 and 634.2 mm, respectively. Most notably, the coefficients of variation for laying width and thickness were suppressed to 7.6% and 11.6%, respectively, values that are significantly lower than industry standards, thereby proving the operational stability of the system. In conclusion, this research effectively resolves the longstanding issues of poor adaptability and the need for specialized equipment in rapeseed harvesting. By realizing the orderly guidance of stalks and the formation of flattened, well-ventilated windrows, the developed header significantly improves laying consistency and drying efficiency. These advancements not only reduce the risk of post-harvest losses but also provide a substantial technical reference for the future optimization and structural design of intelligent rapeseed swath harvesting equipment.