I've started to build the AR3 since I already have a number of encoders in stock. So I'll order the AR3 series motors instead. In order to create some of the castings instead of machining bar stock I've used a combination of the 2D drawings and imported via either an old version of GeomagicCAD or a friend has used Fusion360 on the STL files to grab some of the measurements that aren't immediately obvious on the 2D drawings.
Got about half the 3D printed covers done. Have both Teensy 3.5 and 4.1, Mega3560 and pretty well most of the bearings.
I'm using AlibreCAD to do my drawings. Will use AlibreCAM to machine the castings and other metal parts.