SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

What you have pictured there is the hardest valve to rebuild. For me anyway. The last time I tried, I gave up after an hour. Gravity totally works against you. I just replaced the valve and pretended the whole thing never happened. lol The 1" I can do. The 3/4", not so much.
You're correct on the new parts looking different. They will NOT fit the old valve.
You can try a local parts store such as, Ewing, Site-One or John Deere. I don't know if you can still get the old kit. Maybe find a Hardy catalogue online. Get the part number if you can before going down there.
This valve should be old enough to have the old parts in it. Says '91 on it.
If you can, just swap out the valve. Trust me on that one.

Ok I'm back. I believe that the diaphragm will fit. It's the metal part that doesn't fit.
And I'm not saying that it's impossible to replace the parts. It's just very difficult. I've been successful a few times. It's just getting that spring in there with that big black thing balancing on top of it that's the problem. Then the diaphragm has that skinny groove around the outside of it that has to fit just so or it leaks.
Good luck!