locking the difs means you lock up the spider gear in the front a rear differncial. a normal differencial is made to allow the tires to spin at dif speeds for improved turning. a locked dif will make the tires sping at the same time no matter what. the advantage to doing this is you get an incredible amount of traction with it.

as for a 4-link, there are a number of ways to connect shocks. some people have chassis long enough to connect them directly to the axels. another way is to use clamps and slide them onto the lower link and lock it in place using sets. or, like me, i used hex bar and drilled mount holes through the sides so the shock could directly connect to the link.