Sounds like you need to pull the distributor out, turn the oil pump shaft to point where you need- and then re-insert the distrib so that you have more room to turn it before the vacume advance hits the intake.

After advancing it some more- if it still doesn't run quite right- there is still no need to replace it- just get it set right.

Call around to some engine shops and find out if there is a place near you with a distributor curve machine- you'd take them your distributor and they can setup a custom advance curve matched to your engines specs. Shouldn't cost anything near what a new distributor would....

Just pulling and re-installing for more room though should give you a few more degrees of inital timing- that alone may make all the difference you need! Give it a try!