I think you have your information wrong.

The higher models of 7s there were called Infini's,

But that does not look like a seat design from 86-91

So I did a search on the Bathurst Type R.Which would be the ideal time for that style seat.But I couldnt find any seat pics.
Something like 98-2002 maybe.

Looks like you need to do some research.

They wont be cheap from the looks of it also.