My '96 ends up about 5 1/2 to 6. I put 5 then adjust up from there.
You really shouldn't overfill it too much, or the crank lobes will splash it too much, causing it to froth up and not pump thoroughly, as well as causing extra resistance/drag.
However, 6 quarts will not overfill it much anyway, and it would be safe to just dump 6 in off the bat and be done. The 4.0 and 4.2 blocks are high capacity. Before you put your new filter on, put some in it from your 1st quart so you arent starting it up totally dry.....it will take less time to get oil pressure that way.