I did not find your pictures. You should have posted them right herewith the "go advanced" box.
If the three blocks are a foot apart and are on the side of the boom like cheek blocks they are probably for reefing lines. There may also be an attachment opposite the blocks for a line to tie off on, go up through the leach reef cringle, down to the block, and forward. From there it may be cleated off on the mast or run down and aft back to the cockpit so you can put your reef in from there.
Oops! I found your pictures that show 3 boom bales. Obviously they are not for reefing. There are two options as I guess at it. That all three are for your mainsheet to reduce the load on the boom, or one is for the boom vang and the other two are for the mainsheet.
You have to spread the pull of the mainsheet on the boom as you have mid boom sheeting with it's lower mechanical advantage.
Here is a picture from the 34
http://www.irwinyachts.com/aft-cockpit_files/Cit34/Cit34det1.jpg
and one from the 31
http://www.irwinyachts.com/aft-cockpit_files/Cit31-84/31e4.jpg
They show both options. Unfortunately they don't seem to have a good picture of your boat. Someone else may jump in here and help you out.
Good luck
Joe S