I found a IS300 with a diff (B03B) from what I read this is LSD.
Now my question is would it fit in my 98 Toyota Aristo (A01A) Open diff
could this be a direct swap or could the internals of the IS300 diff be swapped over into the A01A?

 

No the IS diff pumpkins can not swap with the GS nor can the LSD/spyder gears interchange. You will need a MKIV supra or a JZ161 Aristo diff or lsd unit. The Aristo with 3.769 LSD is identical to the Supra except for the cooling fins on the pumpkin.

 

Would I need to do the TT axels? to fit a Supra TT diff?

and are TRD lsd's really clunky?

 

With the Supra diff you will only need the axles if you buy the manual 6 speed diff. It is shaped slightly to the side, so the axles end up being different lengths.
If you buy the automatic Supra/Aristo diff it is a direct bolt in.

Not sure if the TRD diff is clunky. The torsens in the OEM units are pretty smooth even though you can feel scrubbing if your below 20 and make a fast sharp turn sometimes but I think it is kindof cool. I'm sure all torsen or clutch pack diffs do this. I don't think any LSD diff is uncomfortably clunky unless you call a welded diff an LSD

 

The 1.5way TRD clutch diffs are smooth as butter. No clunking whatsoever, as long as you use the proper oil and proper break-in of the clutchpacks and change the oil after the break-in, it will be good.

 

Arristi diff no alder than 1997, newer ones didnt come with Torsen/lsd options.