The easy way to deal with this is with the right wrench, which is a Vim № V-103. Plenty google hits, under $20, and well worth it if you mess with Slant-6 engines more than once in awhile. This wrench can easily be used on either the downsie bolt (holds the distributor plate to the block) or the upsie bolt (holds the distributor plate to the distributor), so no need to pull the dist to get the adjustment you need.