Cool Merc, I'm confused. By metal disc, do you mean boxing plate (should be two in the kit, one for each side)? This is a plate that is about the same guage metal as your frame and is welded on the inside of the frame, making the section a rectangular tube, vice the channel. A good plate should be about 18 inches long for your car. That is why you want to weld a couple of nut plates on for your inner fenders because you cant get in there to install the nuts unless you cut out a hole in the plate which takes away some of the strength you just added.
The body being on just makes the job a little more difficult. By leveling, I mean getting the weight distributed evenly on the frame. Since you have the body on, just put your jack stands at the same height and place under the frame just aft of the front door pillar. This way, when the old cross member comes out, the extended frame rails are not subjected to any twisting moment when you weld your cross member in. It may not make a hill of beans difference, but I like to have my frame level from side to side and front to rear so I can check the new cross member when tacking in. With the body on, you will have to check the front to rear level by using the bottom of the frame rail about mid way between front and rear axle points and I would check both sides. Place rear jack stands at the end of the rear frame rails where the last minor cross member is attached and adjust to attain level here also. An assortment of shims comes in handy here. Having a level floor helps.
Trees
Cool Merc, an after thought to my previous post. Set your jack stands high enough so you can finish some other tasks before lowering your car to the floor. This includes installing your motor, tranny and rear end, assuming you will be making /installing new motor and tranny mounts and setting your rear pinion angle (weight has to be on rear axle for this). Being a lazy guy, I don't raise and lower a project any more than I have to.
Trees
