Thanks! That will help a lot!
I am planning to recreate parts using OpenSCAD, that's as far as my 3D skills go :) Ideally I would like to have a GPL licensed work, but some of the upgrades I am using are CC-BY-NC.
Here is a pic of progress to date. I've got Chylld corners in, all new X idler assembly, a prototype X carriage for Gregs extruder with E3D hot end. Next up is the X motor end, followed by bed some anti wobble bed corners. After that there are some minor acrylic parts to replace, not sure what to do with the cross braces. Maybe use threaded rod like original Darwin? I might experiment with dowel.
I made some minor mods for the Gregs extruder, but it's about 98% compatible with Rapman original. I am going to decouple the end stops from each other, so the axes can home independently.
Then I will look at putting 8mm rods with 50mm spacing compatible with Mendels, and swap in a Nema17 mounted horizontally for the X axis, the idea being to reduce moving mass and maximize build volume.
Alternatively, I will look at replacing the whole XY with H bot or CoreXY type mechanism.