It does bolt straight in as long as it's the 8 bolt hole mounting to the crown wheel out of a series two.

Make sure you use the crown wheel out of the ib5 & bolt your LSD to that & build your box back up.
I've built one ib5 out of an escort Gti which is going to go in my car and I'm going to be doing another one out of a puma for a friend in the next few weeks.