I recently installed a Ford small block crate motor in one of my Mustangs. I added a Canton pan and a magnetic drain plug. On the first
oil change at about 1500 miles, there was a 3/8" glob of very fine, black iron particles (kinda like an Etch-A-Sketch!) on the magnet. The second
oil change showed more of the same, but less than the first change. The third
oil change was pretty well free of the particles.
I highly recommend using a magnetic drain plug, and also a Filter Mag that attaches itself to the outside of the oil filter. No need for these iron particles to continue to circulate throughout the oil system. Cheap insurance along with
synthetic oil after break-in.