oil viscosity and pressure for SBC
This is my own opinion, so take it with a grain of salt, not as the gospel truth. I've always ran nothing but straight 30W in my engines, except when the outside temp is in the teens or lower for an extended amount of time; then I run 20W 20 for easier starting. I've never had an oil related failure in one of my engines, although I've had some varnishing problems from using a cheap grade of K-Mart 30 weight. It was called LDO and I should have known that meant Low Detergent Oil. Big mistake, really dirtied up the engine I used it in.
I would stick to a well known brand, Castrol GTX and Valvoline are both good oils, Quaker State and Pennzoil are fairly good, and I don't know about the rest. I'm currently using Mystik JT-6 (I think it's 6) 30W with very good results.
As far as oil pressure in a hot smallblock Chevy goes, my Nova runs 38 psi at hot idle, and 55-60 psi when I'm workin' it hard. When it's cold, it'll show almost 80 psi on the guage (Stewart-Warner mechanical) and that's too much for running down the road; so I always let it warm up before I drive it.
There again, this is what works for me, and it might give you some ideas.
Randy