What oil pressure to expect from a 318 roller?

Should have over 10 at lowest and 40+ over 1500 RPM although many here will argue it should be lower. I would get a new sender as they are cheap or if you have a aftermarket gauge, install it and tape it to cowl to check. If your pressure really dropped to 0 with engine running it would sound ugly very quickly and not keep lifters pumped up.