How do you tme a fuly modfed 1983 Chevy 350 bored .060 ovr crnk trnd balncd hi rise manfld 650 cfm carb racing cam molly rings 305 heads wperf sprngs HEI ignition can you use a vacuum gauge?

A vacuum gauge can be used to set the timing. I would use a timing light to set it for 40 degrees at 3000 rpm's and then make a pass on the track for a baseline. Then try adjusting up and down 2 degrees at a time until you get the best performance.