Leaking from head bolts

I agree with some of the other guy's here, check the header bolts. Especially the outboard end holes. The factory used studs in both ends for 2 reasons, 1 they go into the water jackets, 2 they hung the gaskets on them which makes an eazy job of installing the manifold/ header.
Last fall I fired my new stroker motor and was convinced I had a cracked exhaust runner in #2 cylinder. After removing the header the port was dry, pressurized the cooling system and realized the stud was leaking. Removed the stud to find a helicoil. So most of the studs break when the manifolds are removed and consequencly the threaded holes get damaged in the repair process, which leads to in this case a helicoil or just a poor fitting stud or bolt. Either way some proper cleaning and a good shread sealant will probably fix this problem.
The reason I know this is that I found the broken stud with a broken drill bit in the center when I got the "N'" heads years ago. I had to grind out the broken drill bit and messed up the original threads requiring me to helicoil the hole. My problem is I forgot I hand threaded the new stud (after 25 years) and you now know the rest of the story.
FYI I use Cometic MLS gaskets and so far I have no head bolt leaks but I also recommend using a bit of hi temp silicone at the water holes. My stroker is built from '75 360 block from a 3500 truck MH chassis .