I think I have the handle mechanism/lock install figured out thanks to azcornman and walterhvogal. azcornman directed me to how to access the retainer that holds the lock in place. The retainer is partially hidden under the weatherstripping. If you look carefully, you can see it in walterhvogal's picture. Now that I have that sorted out, I should be able to remove the old lock and install the new one. Just have to get one of those anti-sag springs. Thanks to all for your help and suggestions.

It's a small world, but I wouldn't want to paint it.