manifold pressure
 

My owners manual is silent on operating limits (other than green arc readings). However the 0-2 Dash 1 says to check them at 1800 RPM and the front and rear should be within a couple of inches hg. It also says that anything greater should be investigated as it could be a clogged fuel nozzle or a cold cylinder.
First, does the O-2 Dash 1 limits seem reasonable for a 74G/IO360G? Second, Anyone have any better limits? Third, if you find your out of limits what needs investigating. Just did a compression check and both engines/all cylinders are getting fuel and they are not cold.

Look for cracks (leaks) in the manifold pressure lines going to the engine indicating the highest MP at any given RPM.

I had high pressure readings on my front engine for a very long time. When we finally found the problem, it was a split nut on one of the lines connecting to a fitting going through the firewall.