Agree with Cubey above, best way to know your engines reality is put in aftermarket gauges.
It has been mentioned in other posts on this site that the dash cluster (Especially in the earlier IDI's) is using more of engine check light sensors to give a pseudo gauge reading, than a real variable sensor and appropriate gauge. So they tell you that you have some sort of oil pressure, some coolant temperature, some vacuum, but really cannot tell you with accuracy how much. Also there was issues with resistors in the dash cluster that can wreak havoc and give false readings. Adding to that is some of your sensors by now are quite old and may not function well. Again giving false readings. For all of this many put in aftermarket gauges to see exactly what is going on to help prevent a failure of the engine.
Take my truck, my brake light keeps coming on and off. Lack of vacuum or low brake fluid can set this light. (As well as electrical problems.) Likely the vacuum sensor is going bad and setting off my brake light. However my vacuum pump is working fine and my vacuum measures correctly. The sensor (Big can on the fender well.) looks to be original. So this puts me in a position of not knowing if this is a false positive or a real positive. So frustrating when you drive around and don't know which it is. I will fix that issue but first need to see what is available or if I have to get a used one. If used that could put me back to here months or a couple years from now. However with a aftermarket vacuum gauge and some comfort my brakes are not leaking fluid, I would know that this is a false positive, not an actual problem.
So sadly the only real way to know what your engines health is to put in aftermarket gauges.
All the best!