Drive shaft to long?

You need to measure it. Slide the spline yoke in and bottom it out pull it back about an inch to an inch and a half and measure from the center of the front cap to the face of the rear yoke where the cap strap bolts on, that will be the center of the rear cap. Make sure you have stands under the rearend, you want full weight of the car on it when you measure. It should be somewhere around 48" or a little more. You will need to call your local driveline shop and have them shorten and balance it.