Keith, the GAIA III is not at all complicated externally (internally is a different story, but you needn’t concern yourself with that ;-). It is just a circular metal foot 1-1/2" tall by 1-3/4" in diameter, and will fit into the spring cavity in the HW-19 base. Each foot comes with three threaded studs, one of them being 1/4-20, the same as the T-nuts installed inside the base for the stock springs. You just remove the springs, and install the GAIA. Simple and easy!
The GAIA is normally used "right-side up" (the top of the foot has internal threads into which the stud screws), but there is no reason why it can’t be used upside-down, which it can be in the HW-19 base. One end of the stud screws into the T-nut in the base, the other into the GAIA foot. And the threading allows the foot to be adjusted in height, by which you can level the sub-chassis. Perfect! Art Dudley reviewed the GAIA III in last month’s Stereophile, if you want to read what he has to say about it’s performance as feet for his Garrard 301 table.
There is another superior footer you may want to consider, the one I chose to go with instead of the GAIA: The Townshend Audio Seismic Pod. It costs more than the GAIA III (but less than the GAIA I, about the same as the GAIA II), and is larger in size. I don’t know if it’s dimensions will allow it to be used inside the base of the HW-19, but it can used as feet for the base. I have a set under my VPI Aries I, and l love ’em! They’ve gotten great reviews in the UK hi-fi press, and by Robert Levi in Positive Feedback.