agree with UD.
generic lock washers fine.
as for the head and bolts /studs.
remember.. the head is soft.. studs or bolts were probably grade 5-8
hit them with penetrant, use a drift and give a smack square on the head with a drilling hammer.
they should come off.
if they act stuck, don't use a long hard pull with a breaker bar, but instead use an impact wrench.. set it soft and let it hammer lightly, then gradually turn the air up. Sometimes you can tighten a second, spray more penetrant, then loosen.