[DavidNJ]

I believe the FFR forces their geometry to fit the stock 4-link. This is, that is the original Ford design, a low cost design for low powered production cars. The three links replace the angled upper links with a single straight upper link and add a panhard bar or watts link for lateral location. The lower links remain angled. The Levy kit attempts to straighten the lower links as much as possible without moving the FFR mountng point on the frame.

The FFR IRS uses the Ford upright (as does the Superformance, Hurricane, Turn Ten/D&D, JBL, and I sure others) which mandates a specific mounting arrangement. Longitudinal and rotational forces are primarily (solely) resisted by the lower control arm. Some other manufacturers (including Kirkham, CuttingEdge, and Prestige) CNC or fabricate an upright, allowing more geometry flexibility.

Net, if you got the 3-link free in FFR's winter sale, that's ok. Otherwise the Levy 3-link or the FFR IRS is your best choice.