Judging from the picture, the differential (case at least) looks to be the same, or similar to the 205mm F20TX differential from the '01-05 IS300. The 208mm differentials used in some of the larger RWD Toyota/Lexus models have a much wider front mounting, and the IS F's differential case has significant external cooling fins. The 208mm (and older larger differentials like the 220mm in the JZA80), use a 3-bolt dampened pinion flange as well, while the 86 seems to be using the smaller, more common non-dampened 4-bolt design.
The 205mm differential is the same as the older Toyota 8-inch rear end used in cars like the A70 Supra, etc., so aftermarket differentials will likely be relatively easy to get right off the bat. Not that the T2 (if that's what it is) will be bad, I love the T2 I've got in my IS250.
Here are a few pictures showing how similar this is to the F20 differential (both open and LSD) from the IS300/IS250:
IS250 factory F20SX / FD20A Semi-Limited Slip Differential:
IS300 F20TX / FD20AT Torsen T2 Limited Slip Differential:
Using this Toyota differential is a good thing, this will take more abuse than most any owner will ever throw at it.
Jeff