Hi there.
If you can get hold of an atlas axle,that would be the best choice as they are stronger than the english type ones.
All the Escort rally boys use them and the lsds are easily available for them.
I have a chopped up 131 axle on one of my cars with an english diff casing in the centre as you've mentioned,but i cannot say how strong this setup is because the car has been in storage since i bought it.
If the setup on mine is no good when i finally get around to working on the car,i'll be going the same route as Mick131 on here and doing a BMW independant conversion. Those are strong diffs and can take alot of abuse.
Get one from a 325i sport though,as they have the lsd fitted as standard.
Cheers,
Wayne.