I have a very early Lyrik 2 step fork that was converted to u turn coil by TFT many years ago (after never ending problems with the 2 step mechanism). Ive put on wieght and now either need a firmer spring or convert back to air. Spring for the 160mm travel don't seem to be readily available. There does seem to be a ready supply of Debonair parts available, but are the likely to fit the original Lyrik? I'm not adverse to minor modifications such as shortening shafts if needed (I have access to machine tools).
If you've gone coil, you won;t be able to go back to air - as tiny scratches inside the stanchion tube will mean you won't get a proper seal.
New uppers and a new air spring assy would be needed.
Sounds like time for a new fork!
I'd call a few suspension specialists and see if any of them stock or can suggest coil springs which might be cross-compatible.