There is a heavy duty tail shaft out there for it, sorry don't know who makes it. As far as low gears there were lots of strength issues with the early crawler gears so I don't know how well the newer ones will hold up to alot of power. I think its based on if its a stock motor or not and the driving style.
A tail shaft kit is made by Advanced Adapters. I wouldn't buy it until you break it. I know lots of people that are running V-8's with the stock tail shaft.
As for the 4 to 1 kit, buy the five gear one. There were problems with the three gears kit.
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