Shift knob removal?

[Scott Fisher <sefisher@domain.elided>]

A friend recently gave me a charming shift knob for my '74 Spider, a
nice quality wood with the silver-on-black cross and serpent medallion
in the center.

Now, the car already has a *very* nice knob, one of those highly
polished mahogany types from Dino  -- the ones that look like something
one might order from a Web site that says you must be over 18 to enter,
if you get my drift.

Still, I thought it would be fun to swap the knobs with this new one,
any gift from a friend being that much more meaningful.  So I tried
removing the old knob from the shift lever in the obvious manner: by
grasping it firmly and trying to rotate it counter-clockwise.

It won't budge.

There's a black plastic trim ring at the base of the, er,
amorous-looking shift knob; the trim ring rotates freely but doesn not
appear to be threaded.  I haven't yet tried to slide that away and look
for a set screw, but presumably that's what's involved here. 

Before I break either the shift knob or the linkage, can anyone provide
me with a clue on how to remove this kind of knob?  Even if I weren't
going to use the cross-and-serpent knob, I will one day soon want to
replace the leather shift boot, which has a short rip in it, and that
will require removing the current knob.

Thanks,

- --Scott Fisher

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