Follow the old advice " while you're down there.... " it would be a shame to do a bunch of work on the top end then have to tear it all down again to address the lower end a short time later. The only reason to skip the lower end is if you're going to sell it, then it would qualify as one of those "totally rebuilt" engines that loses the lower end shortly after the new owner takes possession. Good luck, you won't regret doing the entire engine.
Tombat
