In situations like this it's probably easier just to contact the parts store and tell them what you need, ie. a "Sphinx 55 with an [x] length Z-axis" and have them send you a quote. They do custom work all the time. But don't worry about having to pay an absurd "custom work price". They don't do that. The Sphinx 55 used to be a stock build with the store and they will know just how much to add and subtract to get you what you need.

That being said though, it would be a lot less expensive to buy 4 actuators plus the few extra framing parts you need and just build a simple custom system.

 

Thank you @Rick 2.0
@Jeff Powers this looks like a great build that is right in line with the OpenBuilds mission, to make cutting edge tools available to everyone. I hope this Build will be one that will go on to help others at a fraction of the cost.
This is how OpenBuilds and its caring community is helping to change the world for the better!