Okay, its not a Gilson. It is a Allis, a real Allis Chambers made by Allis Chambers. Its a 1974 416 Hydro, Hmm I have some these already, but what the hay. It came with an extra block and bevel gear box, and all the original manuals and paper work from 1974.
Allis ordered a certain number of the new K341 engines from kohler in late 1973 to put in the 400 series tractor, but a problem arose when Allis found out that a monopoly lawsuit against them was being overturned and they would be allowed to have Simplicity build their Outdoor Power equipment again. The problem was they had decided to make a 410, 414, and 416, but with the suit settled they would not need the 16hp Allis 400 spec'd engines. The 10hp K301 and 14hp weren't a problem in not accepting for delivery, Kohler could move these engines to another brand, but the new 16hp K341 was a new model engine and Allis had made a commitment to buy a certain number of these and could not retract. Allis decided to put more 16hp engines in what would have been 14hp 414 Hydros. That is why you only see Allis 414 shuttle shifts, not hydros the hydros were changed to 16hp and 416 model to use up the engines due to the plant closing and the 400 series model ending the same year it started.