I have found that the initial timing is different for the year of 350 you have. I was trying to run mine at 10 and found out right here that my 68 350 ci had an initial timing of 4, not 10 like my book said.. It made a major difference. I have used 4 as my base line and then increased it untill it pinged. Turned it back a tad and made sure it would start there. Works great.
Slider in Wa.