Your engine has been working like that since 1988 and still running strong. Why the change now? What about the bottom 2 cylinders that get VERY LITTLE oil when idling? I think you are overthinking this.
Take those 4 bolts off and pry that plate off carefully. I believe that only holds the seal. Once that is off you can see the splines so a little penetrating oil will go a long way. If I am wrong somebody will be along shortly to point that out.