On a more serious note, a few more things came to mind.
1) Can you tell me what you were thinking about using for a chest plate? Geoff uses an aluminum plate and mine uses a sheet of 1/4" ABS plastic. I imagine mounting all of the hardware to an actual skeleton would be somewhat tricky.
2) I noticed you mention a "tutorial" regarding Geoff's jaw. I don't know if this is what you encountered, but I did see some sketches that Grant drew up when designing Geoff (see below) and noticed that the setup that he draws is NOT what eventually got built.
3) Upon reading your earlier post again, the parts that you listed were in reference to the arm, not the neck/head, which is what I discussed in my reply. While my observations regarding the parts that you listed not being able to connect to each other are true, my response regarding a potential way to create the neck/head mechanism is still valid. ServoCity no longer manufacturers some of the parts that I used at the time to create the arm mechanism. The updated version of the setup would be as follows:
One servo gearbox...
https://www.servocity.com/html/spg7950a-bm_standard_rotation.html
...which would connect to a 3/8" to 3/8" shaft coupler...
https://www.servocity.com/html/clamping_shaft_couplers.html
...which would connect to a shaft of appropriate length...
https://www.servocity.com/html/3_8__precision_shafting.html
...which would connect to a 3/8" clamp...
https://www.servocity.com/html/0_770__clamping_hubs.html
...which bolts to the side of the top of the arm.
I do realize that you are not at all obligated to follow any of these methods in building your Geoff. However, this is information and I do not mind offering my two cents worth. I don't want to feel like I am forcing any of this on you.