Bear in mind that an old, worn out stock dizzy may not perform as well as a new Tii dizzy due to the slop in the shaft. I've found that the timing fluctuates quite a bit on my old dizzy and you may even experience some complete miss fires if it gets bad enough. Since you haven't altered the CR or the cam, a new stock dizzy may be you're best bet. However, if you don't have any emissions stuff hooked up, the vac advance may be of little benefit.