Raise the vehicle and then support it on jack stands. Make sure that it is level, front to rear and side to side.
Mark the location of the front spring eye mounting bolts on the floor pan. Remove the leaf spring and the axle housing with a socket wrench.
Place the front portion of the driver's side frame connector in contact with the transmission cross-member and swing the back of the frame connector up until it contacts the floor pan. Line up the subframe connector's rear spring mounting hole with the holes that you marked.
Line up the rail of the subframe connector so that it is parallel with the rocker box/floor pan pinch weld. Use a block of wood to brace the connector in place.
Trace the floor connector rail outline onto the floor pan, to determine where the floor pan will require notching. Trim the area marked, outward in both directions, with a cutoff wheel, to allow the connector to fit properly under the vehicle.
Trial fit the connector in place; if it fits properly, tack weld it in several places to the front subframe and passenger side, to ensure that the connector stays in place when you are fully welding it. Repeat Steps 1 through 6 for the passenger-side subframe connector.
Weld the cut area in the floor to the connector tube. Weld completely, at all points of contact with the vehicle, around the front and rear pockets. Paint the welded areas.
Relocate the leaf springs and replace the axle housing. Return the driver's side frame connector to its original installation position. Lower your vehicle.