Oil in the water

So a little background while my camera loads. Found a 90 LA 360 with roller cam (thanks for the advice Rumblefish) had it gone thru including 20 over, Keith Black pistons, 5 angle valve job, port matching, deep bowl blend, clean up 10 on the heads, nice Lunati 224@50, 515 lift (thanks Rusty Rat Rod and Mike at MLR) and had the long block assembled and delivered. Added airgap intake, Demon Street demoncarb, MSD ignition and dist, Champion rad and misc goodies. Fired it up and ran it, checked the fluids and everything checked out. No leaks, no overheating, no fluids in the wrong places, everything looked good. Fast forward 300 miles, engine is taking a long time to come up to temp, may be unrelated. Cracked open the rad and this is what I found.IMG_1217[1].JPG