Forgive me if I asked, but have you verified your timing is correct? In other words verified your timing light is accurate? Also, have you verified TDC with a piston stop and checked that the balancer marks are in the correct location, that maybe the inertia ring hasn't slipped?
Done all that. I’m just putting the intake back together after fixing a small vacuum leak. I also verified cam timing (intake valve opening) but it was degreed during assembly
I’m sorry ,I missed that post .
I have never run the 68 4 sp cam but I have run many bigger cams . I would expect 12-14 @ idle and pushing 20 @ cruise . There will be variables like compression, timing , carb and exhaust system etc…. But under 10 just doesn’t seem right for that cam .
Have you tried another vacuum gauge?