Welcome to MVS! It' not the sealant or seals, those aren't strong enough to lock up the cams. Are you certain the crank is on the mark? With the crank on the mark, I'd take off the timing belt and try each cam one at a time. Are they both jammed up, or just one of them? You should be able to rotate ...

Did you mismatch cam cover from another head? This would be my first suspect. They were machined to match.