This mirrors what my dealer told me. They called me the morning the day the truck showed up with my LS. They had several in the shop, ready for delivery the next day, and several out on the lot, by 6pm. They only had two mechanics on duty, so I don't see that much assembly going on in that amount of time. The mechanic told me he went over my tractor, checking a list of items, and that was it. In fact, they mentioned how they loved that LS delivers their tractors in an enclosed trailer, so they don't have to wash/wax them before delivery...wheels on ready to roll, is how they described it. He added "they make me feel like the Maytag repairman. I check them out, they leave, and I never see them again".
I can prove this with photos. If you google smith enterprise in Dunn NC. He has photos taken at the final assembly in the factory in NC. I think he is one of the closest dealers to the LS factory. Yes you can see the tractors are shipped in crates minus a bunch of stuff. I do not know if the rebadged boomers are assembled there or not.