340 coolant in oil

Why pull the cylinder head just one side? Pull the other one now. If you suspect a leak in the head(s), then have them pressure tested rather than magnafluxed. Also, have them checked for flatness on the bottom surface; you're looking for warpage.

Next step after soaking up all that coolant in the cylinders with paper towels and getting it out of there pronto, turn the crank around and around to push all that coolant up where you can get it ALL out. Then spray the cylinder with WD40 as a temporary measure to protect them.

Drain the oil and examine it.... which should have been step #1. See if it is milky through out and, when you pull the plug, watch closely for the first liquid that drains out and see if any coolant comes out first.

Realize that any leak could be anywhere touched by the coolant.

BTW, I can't quite see the fan well enough. Get rid of it if it is a stainless bladed flex fan. The blades develop cracks near the steel spokes and can eventually fly off and destroy things like radiators.