Yes, I did all of that and upgrading actually worked seamlessly in my old game. The issue here is purchasing the guar on a new game.
So, I added some info above, though I think it was after your post, Jac..
It worked when I reverted back to version 1.03, I now have the topics to mount the guar. So, now to test if 1.04 works when upgrading on this new game.
It worked no problem upgrading on my older game...More info to come.
edit: Upon upgrading to 104 while already owning a guar from 1.03, the mount topic now appears on my guar. Hooray! Now, I'm not sure if this is 1.04 specific or just my game. It'd be cool to hear from anyone else who has bought a guar for the first time with 1.04. I'd be interested to know if the mount option showed up on the guar.
While I was testing 1.04, I tried using startscript ab01guAddTopicsScript but when I checked my guar, I still didn't see the option to mount.
Anyway, it's working fine now but, perhaps it's worth looking into in case it's a problem with the mod and not specific to my game.
You're welcome to point and laugh at me if it's only me who has the problem.