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I believe chassistech.com has a bolt in 4 link, Jegs also has had some, you will have to fabricate the brackets to mount them to the frame.
also check with fat man fabrication in Charlotte, NC for the brackets??? Fatmans does have a 4 link complete for around 1100.00
The number is 704-545-0369, ask for Kevin.
They have them for ifs but I am not for certain they have them for I-beam.
Also streetrodengineering.com may have something.
Mark