318 Idling fine then started clattering....

30 psi hot is pretty good. I did have a 318 that dumped 3 lifters at the same time and made a hell of a racket but I still had good oil pressure. I switched all the lifters and it lived a long healthy life. its pretty rare you lose more than one lifter at the same time, but it can happen.
sometimes it takes a minute to get really cold oil circulating and for the lifters to pump up, especially if its 40 or 50 wt. I like to use 30 weight in the winters here in CO