MS112 would be the go if you want to keep a solid rear axle
you will still need to swap control arm brackets as the crown has only 1 upper control arm and the LX81 has 2.
but I would and DID with an LX81 I had years ago fit a MX83 IRS
its a fair bit of work as you have to unpick the panard rod bracket from the body and reinforce the chassis where the diff cradle bolts up but its much better than any live axle