This is a Detroit Diesel big bore (large bore) 6-71 blower case. The large bore case rotor bore measures approximately 5.778" id(whereas the small bore 671 measures approximately 5.75"). I included a picture of this case showing that it is a large bore, and the part number also confirms that. The housing looks to be in good usable condition. All of the bolt holes are good except one, which needs a helicoil. I hand threaded a bolt into every hole to make sure the threads were good. Four of the top holes have been helicoiled and are nice and solid. The fifth has the factory threads and feels good. The sixth hole also accepts a bolt and gets tight, but the threads are visibly shallow, so that's the only one that should be helicoiled. I'll also be selling the end plates for this blower on a separate eBay listing. Please ask any questions before purchase.