Donald Gillies wrote:

I have a Suntour Cyclone 1st generation derailleur (the one that's
campy-like with embossed "SunTour Cyclone" on a black nubble
background.)

I have both a racing cyclone and I have a GT derailleur cage from
another suntour product. I'd like to put the GT cages on the racing
derailleur. However, upon opening lower pivot body it seems the
spindle that attaches to the non-GT cage might be riveted. This is
very surprising because the GT cage is clearly screwed to the spindle
with a 2-slot recessed bolt. I expected the racing cyclone to use the
same cage attachment as the GT cyclone.

Has anyone done this swap, or does anyone know how to do this swap??
Thank you.

No can do. Try this:
http://www.yellowjersey.org/cyclone.html

(Note my tool you don't have)
The upper roller will track better on the short model

To service the lower pivot on a short Cyclone if you are so
inclined:
Remove the cage stop
Let the spring unwind
Remove the spring cap
Remove the spring, noting position.
Unscrew the cage from the pivot.
Clean, lube reassemble.

--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971