the SM 420 has the lower 1st gear than the 465and if your using it in that Willys they are almost indestructable and will give you the crawl ratio you want. however the parts are getting a little hard to find when you break something, the 465 is a little bigger and stronger and the parts are available but 1st gear is not as low . Both trans are 1to 1 in high gear so no advantage is picked up on the big end. The NV 4500 is the hot ticket with compound low and overdrive. But it is expensive. Tony
