J.D.
Mine were 2 years apart and we had the same problem for about the first 6 months (in a really constant way) and about 5 more months on and off. Although it sounds like my son was more aggressive- he would hit and try to headbutt the baby. He would take toys out of his hand and sit on or knock him down when walking or crawling. I thought I was going to lose it and was asking for advice from all.
What I learned is that I just needed to keep on doing what I was doing. It just takes a LONG time to adjust.
What I was doing...probably all things you have already done/heard of
Giving extra attention to his needs, hugs, cuddles, playing time
Talking about how babies are and what they need and having him be a helper and praising that A LOT
Time out for any attempt at hurting the baby
(He responed VERY well to this one) Telling him "your brother loves you so much. He is so happy you brought him that toy. Look at his smile. Can you make him laugh again?" and stuff like that
I let him play with all the baby stuff as much as he liked.
My boys are now almost 3.5, almost 1.5 and I'm 5 mos pregnant. The boys get along very typically. They are usually good and fight over toys now and then. Rarely do they hurt each other. Most of the time they are just chasing each other around. It's totally cute. :)