Jeep Repair: AMC 360 Tuning, hairline cracks, vacuum leak

Question
Good afternoon Ron.
Having now enlisted a number of reputable mechanical workshops to unsucessfully determine the source of the a misfire / hessitation at cruising speed. I now seek further expertise to identify my problem.

The vehicle is an 82 cherokee fitted with 360 ci 4 barrel carb, aircon, p/steer and 727 auto. At idle the engine misses and hunts, under light accelleration or whilst cruising it coughs., Only under full accelleration does the motor perform well.

To date the distributor checks out fine as does the resistance on the cap, leads and plugs. I seem to feel it could be a vacuum leak stemming from the underside of the valley cover and head intake mounting face. My question is how does one check out this suspicion without removal of intake manifold? Or could the problem be elsewhere, am I barking up the wrong tree.

Answer
If you indeed do have a vacuum leak, it can be verified using a vacuum guage.  Any motor manual will have a section on the various vacuum readings and what they mean.
You might have a crossfiring distributor cap as well.  Hairline cracks are usually the sign but not always evident.
If you have not replaced the cap/rotor, plugs wires and plugs, it might be worth the investment.