360 oil pressure relief valve spring replacement instructional?

That would be a rare failure. I would first change the oil pressure transmitter before going into the oil pump assembly. It's a 5 min job. If you can, borrow one from another car and see what's happening.

 

I will second the oil pressure sensor, these do go. I've also had to replace a stepper motor in my gauge cluster due to similar things happening. You can use a 24mm bike wrench (like the park tool scw-24) to loosen the sensor, and you will not have to remove the oil filter. Only a very small amount of oil will seep out. I have an extra working sensor that was only used for a year if you are interested.

 

Yes, sensor. That is symptomatic of a failing sensor. Pressures vary from normal to max intermittently.