Thanks for your reply. I found it interesting that you'd mention Gibbs software because a machine-specific version named Gibbs SFP Express Programming Software was factory installed on this machine. Here's how that appeared in their promotional images on the machine's control panel.

But that SPC version is limited to 3 or 4 axes.

I will want software that's workable though I understand that to buy one of the claimants to being able to generate the absolutely most efficient tool paths and speed variations along that path, very high cost products are required. I'll be most interested in lower-tier priced 5-axis software. What product brands would you suggest examining to find which best fits that general description?

I've been looking at large "slewing bearings" through which the driveshaft and adjustable-angle gear set's power can pass. I imagine the first slewing bearing attached to the head, enclosing the original spindle, with a worm drive to enable controlled-position rotation and power transfer. The first adjustable-angle bevel gear set would be as high as possible under the CAT 40 tool holder, limited by its required ability to rotate from +90 degrees through 0 degrees to -90 degrees. That pivoting section would be enclosed by a second slewing bearing positioned by a second servo or stepper motor and a second identical adjustable pivot angle gear set. If both adjustable-angle bevel gear sets are set to 90 degrees, vertical height loss caused by using this attachment would be at its minimum value. I think and hope that length can be significantly shorter than Tri Tech's product.

Some really clever slewing bearing race and cage configurations exist. I especially like one I've seen illustrated which alternates rollers positioned on axes about 90 degrees apart, forming two concentric and interleaved roller sets which load against roughly 90-degree separated thrusting race faces. I'll try to find an address where that configuration can be viewed and edit this note by adding that link.

Before anyone points out the obvious fact that my automatic tool changer won't be able to work with this attachment, I already know that. 99% of my use for this machine will probably still be 3-axis work. I'm also aware that every linkage and force extension reduces accuracy. So being able to maintain 0.0005-inch accuracy will disappear by adding two worm-driven slewing bearings and their housing's additional length. So far as I know, 5-axis machines are always less rigid and so less accurate than otherwise-comparable 3-axis machines. That accuracy loss is just another cost of swimming in those waters.
John