I retrofitted the swivels on both side of my non-westy Syncro and I LOVE
them (bolted them in - welded would have been better).  The height
increased only about 1/2 inch, and didn't seem to get too close to the
windshield for my short legs.  Also, I don't have to open the door to
fully swivel the driver's side, although I do have to work the armrests
around the steering wheel a bit and work the seat back and forth on the
rails.  I have a Carat flip-up table installed and when the driver's side
swivels around I'm sitting right at the table.  Crack open a cold one!

One thing to watch out for is the groove in the swivel's sheet metal pan
that accepts the latching arm - mine was opened up and bit and so the
seat has a bit of angular play even when latched.  A sleeve to beef up
the arm at that point would fix it.

In short, I think they're very cool - go for it!

-Steve