by the way there is an easy old school trick that is cheap and works well for adjusting and or just checking valves. Just take a pair of stock crappy sbc covers and cut the center out of the top. Then plop it on there and fire it up... you can see all the rockers and make adjustments without the smokey oily mess!
check your base timing in 2 ways. first use a timing light with the advance unplugged. Second, you can use a vacuum gauge and just adjust it till you see the vacuum hit its highest steady point then make tiny adjustments from there.
Personally, and It may be unfathomable to some people but I can get real close just by an "ear tune" cause I have built so damn many sbc's. After wards Ill double check with a timing light and Im almost always within 1-2 degrees. That comes from a LOT of shop time...lol