1) Download R1900/2880 service manual.
2) Disassembly everything but leave carriage with HEAD, CR motor, CR encoder, CR sensor etc, APG system, pump and capping station.
3) Cut unnecessary parts of frame.
4) Rest is up to you. You can do it in so many ways.
Just think and choose the best solution that fits your needs.
Personally I choose CNC construction profiles for frame.
Linear guide and chain belt to drive the bed. In this approach you can buy everything you need in one shop with CNC parts.