oil change on my 360

I'd start digging deeper. Pull the dizzy and look at that, and the intermediate shaft and the gear cut in the end of the cam which drives the quill, and look at the bushing, too.
Since they are magnetic slivers and flakes, I'd consider places where iron/steel would wear first. Pull the v. covers and make sure the rocker shafts are oriented properly. Look for more debris evidence. Try to examine the cam lobes. If anything looks suspicious, pull the rocker assemblies, & p-rods, and examine the lifters. Keep everything in order to simplify reassembly. Be prepared to pull the pan, too, if for no other reason, to clean it and the oil pickup.