What are the true effects of advancing the stock cam 4* on a SD motor? I'm building a new motor with a goal of maintaining low end torquewith stock cam, worked GT40 heads and a ported lower. I have an '86 and an '89 cam - any difference between the two?

yes thers a differance, the 89 is better slightly

as for advancing it 4* yea thatll give you low end, but these cams suck enough that we dont even pull till redline, when i planned on reusing my stock cam my plan was to retard it 2 deg