Given that I now have both the newer VM and image from the Ubuntu Pharo PPA, and the VM and image from PBE, opening a file browser and clicking on an image saved from PBE fails, because it wants to open the newer VM.
No problem. I'll just use pharo.sh from the CLI. Oh, wait. It always wants to use Contents/Resources/pharo.image.
No problem. Fix pharo.sh so that it accepts an optional parameter specifying the image name to open, sans path and ".image". Not especially brilliant, and bash experts might have a better way (or caveats as to why this is a bad idea), but now I have something that behaves, with very few changes to the original pharo.sh:
"./pharo.sh" opens the default Contents/Resources/pharo.image "./pharo.sh myPharo" opens Contents/Resources/myPharo.image