Yeah.. no need to swap internals.. just replace the diff cover. and use the appropriate axles with the correct flange (5-bolt or 6-bolt.)
Also, Any r200 diff will swap into an s13 housing.
This includes R32 skyline diffs, S15 helical diffs, Z32 NA diffs, J30 diffs.. anything with an r200. Just make sure you get the right output shafts and axles for the diff you use.
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