I see a lot of drag cars with these " 4 link " rear ends in them. From what I understand at present it is mostly done to add strength to the rear end of the car so the diff doesn't twist or flex under extreme load... correct?
I understand under large horsepower and torque situations this type of rear end would be vital but... I saw one built into a VL with a stock turbo motor in it... is this just wank value???
Does anybody know of a website that better explains the setup or a how to do???
Cheers.

No not for wank factor, its a progression building a drag car. Get ya chasis sorted then bring ze powa.

4 link allows the diff to rotate to give more traction under acceleration

4 links stop the diff from rotating, to minimise diff roll and playing hazard to ur driveline and stuff.

and to hold ur diff in place when u bag ur luxy and wanna get rid of those nasty ugly leaf packs

It's not so much that they stop/prevent diff rotation, rather make use of the rotational forces to aid in traction. Depending on how the bars art setup you get either body squat or anti squat. If you have the bars pointing below the COG the body will tend to lean backwards & transfer body weight on to the rear tyres. If you have the bars pointing above COG the rotation of the diff will act against the bars & push the diff housing downwards planting the tyres.

Dave Morgan wrote "Door Slammers: The Chassis Book" and Chris Alston wrote "Drag Race Chassis Tuning Manual".
Both extremely easy books to read and probably set the bench mark for understanding how the suspension makes a drag car work. Both books have been around for years.
As for a four link, 15uzu pretty much sums it up.
They are a science and take an awful lot of work to setup so that they will work.
As for how to do, LOTS & LOTS of planning before you even touch the car.