Okay,I changed the distributor today and got the result I wanted.At full advance with the old one,18*.Took one out of a box I had laying around,set it at fully advanced where the old dist. was,got 27*.So,in effect gained 9ish degrees of timing adjustability.Not that I really need it,but I've been bored and nit picking at problems that don't really exist this week.I spoke with a friend who is a Nissan master tech,and he said the easiest way to check for a stretched chain is remove the valve cover and look down at the tensioner.Knowing that there are about ten "teeth" (for lack of a better word) on the tensioner,count the teeth that are exposed.If all of them are,yeah,your chain is pretty worn.I have not done that,and probably won't until I get bored again.
@gomba-try a different distributor if you have access to one,although it sounds like you may have other issues as well.