I am replacing the old W-C head with the Raritan PHII model. The existing plumbing will work and the toilet fits nicely in the space; it's only slightly larger and I have it positioned on a bias. It's not a direct replacement as the bolts are in different locations, but it's a simple matter to fill the old bolt holes and the new head has a plastic trim piece that hides the old holes (and the base of the head) anyway.
Practical Sailor reviewed the head favorably and it's pretty affordable.
I don't have any input on the newer W-C.
