I use XT90 for connectors.

As for the diff shim, the point of raising it is to increase the angle of the CVD and change the plunge of the dogbone to the outdrive. Combined together, these cause more of a bind that tends to stiffen up the rear by having the drive line push the tires down on power for more traction. There's a lot of physics I haven't 100% looked into that will fully explain it, but that's the short version of it.