https://www.mgexp.com/forum/mg-engine-swaps-forum.40/affordable-lsd-for-salisbury-axle.4307261/
http://www.mattlewisracing.co.uk/product.php/2859/1408/limited_slip_differential_volkswagen_02q
I thought that I would update this, I bought one of those Blackline LSD's two years ago on a Black Friday sale when it was at circa $500. Although there is very little info about them on the internet Heathrow Transmissions who are the UK's largest rebuilder of MGB gearboxes and axles fit these in preference to Quaiffe, likewise Hardy Engineering do the same. I was told by Hardy Engineering that there are often problems fitting the Quaiffe simply due to the splines not being machined properly in the LSD. Although you are told to renew the oil after 500 miles to drain out any swarf, they have never had any problems or warranty claims.