WOW, that's a big dent! The good news is it doesn't look like there are any major creases in it, but a dent that size will have some expansion. I would use a deadblow hammer instead of a rubber mallet. If you gotta buy one anyway you might as well get the better of the two. You are proly going to need to remove the breasthook to get to the backside good as well.
I would drill out all the rivets along the panels from the bow back to about 6-7 inches past the dent. It is easier to pound out two individual pieces of metal than one big one. Chances are you will need to re-rivet anyway, so you might as well make it easy while doing the work as well. You may have a little expansion that you will need to work out with a dolly and hammer otherwise you may have a slight bulge after the dent is knocked back in place. Maybe not enough to notice tho. If it were me and the rivet holes lined back up I wouldn't worry about it, a small bulge would just be cosmetic anyway.
Very easy to do, proly take about 3-4 hours max, proly even less.
On Edit: I didn't realize it was dented on BOTH sides! Yea, that's gonna take some time, the port side has some pretty big creases/dimples. Still doable tho with a deadblow, dolly and a couple of pieces of hardwood dowel you can shape the end if you need to for the keel area. I would say 6-7 hours for repair.
