The rig I built befjre mybfirst 80 had an Atlas 4spd. They are the sheit and I would have kept it for my 80 but there is no way to bolt an Atlas to the back of our transmissions. If there was, you be able to read all about it in my build thread and, I’m sure, many others.
I wish and pray for someone to make an adapter for NV4500 to 1fz for the low range and a place to bolt an Atlas to but it hasn’t happened yet.
You answer is in the classifieds or at least it was a few days ago. Some one is selling a GM 6L swap kit including engine, stand alone controllers l, trans, mounts, adapters, etc. all that’s missing supposedly is some wiring stuff to connect the power train to the body electrical. All on a pallet for $10k. An Altlas would bolt to the GM automatic nicely.
With gears that low, horsepower, and big tires, tons will be next after you start breaking axle parts. We either dig very deep in our pockets or we exercise a higher level of patience.