I always remove the prop shaft from the gearcase and put the bearing head back in. Put the skeg back on with the gearcase gutted and tighten the screws. With it mounted in the lower unit, you have something to hold onto. I then remove the seal with a seal puller I made from a piece of a damaged drive shaft I had. Thanks to Ron Baker for the idea of making the seal puller. I had destroyed the one I bought from Advance Auto Parts trying to pull the seal out of one of my QD-16s. So far, using the gearcase to hold that bearing head has been the easiest solution I have found for getting a good hold on it to allow the seal to be pulled. I did crack the seal pocket on one that was previously damaged, but that is the only problem I have had. Maybe this will help.
Here is a photo of my seal puller.
-Ben
OldJohnnyRude on YouTube