"the client's irrevocable trust EIN and not his social security number. Can I report the K-1 on the 1040 return"

Keep in mind that the reason someone forms an irrevocable trust will include that its holdings are separated from the self. It's similar to how you find your "self-employed corporation" clients might tend to commingle financial activity. They/you need to honor that separation. A revocable trust is a bit different and is not by default its own separate entity. There are tax treatment reasons and there are legal reasons (such as holding title to deeded real property). If you are going to have clients with trust activities, you will want to understand these details. Often, what the taxpayer thought they were doing, and what got put into place, are not the same. That's why you get the paperwork and don't just listen to what they tell you.