This is how I free a very stubborn coupler. Hopefully it helps someone trying to convert to dripless packing.
This is on an older Malibu, but principle is the same on most Vdrive and DDs. Some of your older Centurys use different methods to key/index the shaft, so be sure to uncouple shaft and figure out how the shaft is joined to coupler.
In this case you have to remove the nut(1 1/16" socket on 1" shafts)inside the coupler and loosen the set screws, there are two hex key/allen heads in the coupler.
Next I use some long 3/8" bolts with no shoulders and a socket to preload the living crap out of the shaft.
We have a sweet slide hammer at the shop that was there before I started. I have searched the web for one just like it to no avail, but this is the closest I can find(If anyone wants to machine a better one I have some ideas)
Thread the puller on and slide hammer away. In this case this STILL wouldnt free the coupler.
SO, heat to the nibral/brass coupler while your buddy/wife/kiddo slowly turns the shaft and occasionally puts some work into the slide hammer and bingo, shaft pops right out of coupler.
Most are a lot easier but if youve got one that fights you I hope this helps.