That aluminum is hardened and the wood block will most probably wedge into the mast and the dent won't budge. You might consider making a hardwood block that is about half the size of the inside of the mast (opposite the dent). Then use some sort of metal backer on the dent and metal wedges to drive the dent out. My only real experience is with a small dent I had near the mast track on my H16. The track was squeezed too close in this area. I put two peices of hard 1/16" thick metal plate in the track and then drove a screwdriver inbetween them to spread the track. It was very difficult to spread even this small area, but it did work.
Good luck,
Jack Hoying