Hi,

On your J,
- separate the Green J curve (not surfaces, only the curve)
- with a sweep with 2 lines (top horizontal and down horizontal) and 2 rails (inner and outer curves) you have the front surface.
Do the same thing with red J curve.

You have now your J solid after joining the surfaces.

 


Another possibility is to create Solid text and flow those solids next.

Have fun...