I have used chunks of various sized many times. Initially I used 1x1 or 1x2 inch, and more recently have used about 1.5x3 inch. To put chunks in I remove the feeding tube and use tongs in insert a chunk, smaller chunks I put two of the larger one of. I am careful so that I can re-insert the feeder tube and close it. I now have a bandsaw so I can easily cut the chunk to any size I want, I also remove the bark. Since I have a large pile of oak firewood the last few years has been mainly oak and some almond. I just bought a bag of Hickory chunks and will be trying those as well.
You will be surprised how fast chunks can burn, I suggest you give them a good soak first to slow down the burn rate. I start with regular size chips and get a good bed of hot ash, you can do this during your preheat before you add meat. Remember that different wood types give off stronger smoke, I had that problem with the larger oak chunks, so had to stop using them.
