340 Duster oil looks milky

This is a good read on cam installation and break in....just info that's useful for new cams. Go's over install, lifters, lash adjustment, timing and break in.
It may have nothing to do with your issue at this point, it's just a good read.
http://www.hughesengines.com/Upload/productInstructions/camshaft_instructions_Aug_2019.pdf