65 Valiant 170 Still no activity from the ignition key

I don't think it's your starter relay. I think your problem is (still) in or very near the ignition switch. I can't tell exactly what you mean by I replaced the ignition switch and lock cylinder just in case when I did everything. If you mean you replaced the switch as a part of trying to diagnose this problem, then look closely at the wires where they connect to the ignition switch and where they go through the firewall. If you mean you replaced the switch on general principle just to have a new one when you were reworking other parts of the car, then the switch is your first suspect. Put the original switch back in and see if that fixes it. Your brief-flicker-of-the-oil-light as you turn the key strongly suggests there's something the matter with your ignition switch, to me.