jamesincYeah if you are willing to pull the motor out either way, I would just replace all the seals and gaskets and then put it back in. I'd do at least a compression test first though, in case the bores are very worn. At that point it would probably be cheaper to find a used redblock that is less worn, although that has its own challenges as you probably won't know what condition the replacement block is in unless you open it up or the seller did a comp test.
The engine has done 450k. What is getting meto even consider this, is how good the body is. As someone has said, the body and paint is way more expensive to fix.