Finally (finally!) had an afternoon to do this. The part numbers above are the correct replacement "clamps" for this application; I guess if your cable ends look like mine then those are the clamps for you.
I ended up cutting off the old clamp with a Dremel. There is a very small tab (visible in the second pic) about halfway down the shaft of the plastic cable end that prevents the clamp from sliding off. So right or wrong I carefully cut off the clamp and was on my way.
Below is the old and new clamp. The black piece missing from the old one necessitated the change. The orange spring assembly stays retracted until the clamp is in position on the cable, when retracted the ribs lock in to corresponding ribs on the plastic cable end.
Here we have a view of the ends and their relationship to the transaxle. This is with the drivers side wheel removed, peering through the suspension, towards the front of the vehicle. At the bottom of the pic you can see the transaxle housing, towards the top left you can see the counterweight which overhangs the shift tower. I didn't change the other clamp due to time constraints, but because the shifter is *SO* much firmer with much less slack I will be changing it soon. You can also see the plastic end of the cable is ribbed, this allows for minute adjustments to help the feel of the shifter.
This is with it all back together, note how the orange spring piece has been released and therefore clamps down on the cable end.
All in all this is max of an hour and not too bad a fix once you figure out how the bits work together.
Thanks to everyone for their help!