I just did this job on sunday on my 90 lumina. I couldn't find either of the bleeder plugs. I just kept starting and stoping it with and without the rad cap. I removed the hose from the pipe that comes out of the water pump for a bit as well but didn't get a steady stream. After a handful of tries the system finally cleared itself out. Someone really needs to post pics of these bleeders. I saw something on top of the thermostat housing that could have been it, but didn't know and didn't want to unscrew it.