I am working on restoring a 1959 IH B275. Can anyone please tell me how to replace the governor diaphragm on a CAV BPE-4A inline pump? I removed the cover and spring, but don't know how to release the stop control rod so it will extend enough to remove and replace the diaphragm.

I would like to rebuild the entire CAV pump, but there is no help to be found on this style pump in the US. I have all the needed replacement parts, but every shop I talked to here, their standard answer is just bring it in to the shop. That wouldn't be so bad if the shop were next door to my house, but with the tractor not running, taking it to a shop in another state is simply impossible. If anyone is familiar with this pump and can give me basic directions to rebuild it, that would be great. I would settle for just replacing the diaphragm for now since it was running pretty well until the diaphragm ruptured.
Thanks in advance for any help.