There are no easy swaps nor any kits that I know of to do so. I have seen a couple owners who've had custom rear subframes mad or the stock one modified to fit domestic housings... While I like the options it opens up the cost and effort isn't worth it to me; The stock differential is a beast and can take a lot more than your engine is likely to be giving it. You'll most likely need to source the shims and any other components from Toyota. The only part I've heard of anyone going elsewhere for was a custom made crush sleeve for preload purposes, IIRC.
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