Ive got an exterior wall with a chimney that protrudes into the room. The wall was originally plaster, but when I took off the lovely 70's paneling, there was only a crumbled mess.

We put up new drywall on the wall, but the chimney was in good shape (at least externally). Now, I'm not sure how to address the joint between the drywall and the chimney plaster. Based on my experience with mudding drywall, I know I am unqualified to use any plaster type products that cannot be sanded to correct my sloppy work. Will tape and joint compound work in these corners since half the joint has drywall to cling to or should I use some sort of plaster patch? If I have to go the plaster route, is there any sandable patch product?