Looking for advice on initial timing number. Newly rebuilt 400 sbc. Bottom end is stock. Aftermarket heads: iron, 72 cc, 210 cfm intake flow. Hydraulic flat tappet cam: 443 lift, 214 duration, 110 separation. Aluminum dual plane intake: 165 cc runner. Carb: 600 cfm dp. Stock hei distributor: 20 deg. built in. Running with a manual 4 speed transmission. What should I set idle timing at? Have messed with 10 to 18 deg. btdc. Cannot get a vac rdg above 14-15". What is an acceptable vac rdg & where should my be initial timing? Any thoughts?