Why would you need an adapter between your 292 and the sm420? should be a direct fit. I think that you will be happy with a ranger O/D they are pretty robust are easy to shift, and have a high over ratio like a nv4500. You can use it to split the gears if you like to play around or just leave it in O/D and shift your main trans like normal. It will definately help you on the road if you are still running the the original eaton!