Want to build a 77 360 suggestions please

Steve Agrella said
I’m not sure what the condition of this engine is in, I was told
it was rebuilt 12,000 miles ago, not sure looking at the paint on the motor not sure that really happened or not.
The motor right now sputters and misfires when I get on it, checked the timing its at 12 degrees ideling at 900 rpm ??
I would like to get into low 13s with this car

Sputters and misfires?!?! Start with new plugs, wires, cap & rotor.
Check the state of the carbs tune!
Readjust the initial timing (vacuum advance hose disconnected and plugged off.) to 15*. 20* max.
Limit total timing to 52*’s. (Vacuum advance hose attached.)

Report back what you think then.