Yes, the single viscosity 40 is too heavy. These days I prefer to run 15w-40 diesel engine oil due to the fact that the ZDDP levels in conventional motor oils is been drastically reduced over the past decade or more. The diesel oils like Delo etc still have about 1200 ppm of ZDDP. ZDDP is an abbreviation of that stands for a blend of molecules that from a crucial sacrificial barrier between tight tolerance metals such as cam bearings cam lobes. These old school, flat tappet, push rod engines need that ZDDP. Cam shafts and cam bearings can fail prematurely without it. Of course you can play shade tree chemist by adding ZDDP additives from STP and others to your conventional oil, but I prefer to use what's already been blended by the pros. 15W-40 is great in older gas engines.
Now, what you should see on your oil pressure gauge when the engine has worked up a good, hot lather and it's idling at true curb idle, is the oil pressure drop considerably from your cood engine reading. Like Scott said, if you see at least a steady 10 psi then, that's plenty. The other time to be really mindful of your pressure is during a sustained highway cruise where the engine is running @ 2800 revs for minutes at a time. Again, your gauge should be showing at least a steady 30 psi then. If the gauge needle fluctuates noticeably to the point that you even begin to here lifters tapping, that's an indication of top end oil starvation that could well be the result of one or more failed cam bearings.
