Six Sigma can indeed be effectual for you or any other company. I'm quite sure you have heard of SPC, or statistical process control. The heart of Sigma Six is just that along with a patterned approach to using SPC in identifying defect origins. The desired result is fewer defective products. Sigma Six can be used for any type of production and is not intended just for painted products.
The polyester-TGIC powder will adhere fairly well to clean metal substrates, but with an iron phosphate pretreatment, both adhesion and paint durability will be appreciably enhanced. The metal profile generated by shot blasting aids adhesion, but be aware that residual shot embedded in the surface may initiate galvanic corrosion on some substrates. Since you have such long pieces, I suggest a cabinet washer with a metal mesh belt to convey parts horizontally through the cleaner/phosphate and (single or double depending on water quality) rinse spray zones. Follow this with water blow-off and a drying zone.