I have the FLA 4x4 and it uses 3030.
You probably mean you want to use the cncrouterparts R&P system, which Fineline buys from them.
I very much like the FLA-300 4 x 4 design. The fundamental idea I like is that the X gantry is a single 3030 beam, directly tied to the carriages. The bed is hung below the Y rails. This means that the gantry is not suspended up from the Y rails by some structure, and it means that the gantry is just the beam, with it's R&P rail/rack.