There's no morph for this one. I transferred a G8M rig and weights, adjusted the rig to fit better, and smoothed some of the weight mapping. I also added rigging for the doors and extender on his chest. When using poses sometimes the doors might appear slightly out of position. If you want to make adjustments to them you will need to unlock the translations and extra rotations for them in the Parameters tab. I locked the ones that weren't for basic functionality like opening the doors to make it a bit more straightforward.
I also rigged his waist cloth and the cables on the back of his head as well as added his bomb and rigged it. Two sides of it can extend and rotate.
MK1 Cyrax: https://mega.nz/file/8X1l0ISJ#miEdtMoYjjcjGVLJCHy2fYrVo2INclyLZxW-2Uh_tZI