I haven’t had too much time to work on her lately, but am leaning toward the intake manifolds not being fastened snugly. When I removed the manifolds, it appears the previous owner’s mechanic must have had some issues, as instead of a stud, it had been replaced with a bolt, AND two of the studs were very loose. After attempting to tighten ever so slightly, they came out.
So, I’m in the process of locating some step studs from the standard 8mm to a 10mm. I’ll drill and retap the heads to accept the 10mm size, while leaving the 8mm for the intake.