I wouldn't worry about rigging the cunningham, unless you are racing you really don't need it. The boom downhaul performs basically the same function.
The 1977 (along with all DS models 1958-85) was setup originally for roller-reefing on the boom. To use it you un shackle the mainsheet block from the boom and pull the boom slightly aft (goosenck is spring-loaded) and with the sail raised, twist the boom to roll in a reef as you gradually lower the sail as it rolls up on the boom. Here is the problem..... the sail will cover the mainsheet attachment bail! So, you needed a roller-reefing claw to temporarily attach it while reefed. (see pic below). Now the unvarnished truth...... the roller-reefing never realy worked very well anyway! Even on bigger boats most owners have gone back to good old-fashioned "slab-reefing" ie: reef points. I did so on my DS II in 2000 after struggling with the roller-reefing for 4 seasons. (Still, if you want instructions on how to use this feature, let me know!)
My advice, bring the sail to a sailmaker to have them add the reefpoints. it cost me around $65 in 2000 (I;m sure cost has gone up, but hopefully not much) and another $30-$50 or so for various blocks and cleats to rig the jiffy-reefing setup (there are ways to do it for less, but my setup works good.) You can get a kit from SAILRITE.com to add the reefpoints yourself if you have access to a good, strong sewing machine, but I'd still go the sailmaker route. My boat is setup similar (but not exactly the same!) as the newer 1986-89 O'DAY DS III, which did come from the factory with reefpoints. Below is the page from my expanded Owners Manual for the DS II showing how my boat is set up.
Here are instructions for reefing:
To Reef:First, release the main halyard until the reefing tack cringle, has reached the boom. Second, pull reefing line to bring the clew cringle down to the boom and to also pull it aft to tension the foot of the reefed sail. Once the reefing line is tight enough, secure to cleat forward on starboard side of boom. Fourth, tighten halyard. Fifth, wrap the 3 short lines that run through the reef points around boom and tie off (use a “reef-knot” or slip-square-knot to allow easy and quick release when shaking out the reef, aka: un-reefing the sail).These lines are 3/16" braid, 2' in length and are run through the reef points (small. holes in sails) tie a knot in the middle of each line on each side of the holes, let them hang down until ready for reefing. I keep these reef point lines rigged all the time.
There are other ways to set up this style of reefing, larger boats sometimes use a reefing hook attached to the gooseneck to secure the tack cringle, and rig a reefing line only for the clew cringle. That was how we rigged our old CAL 21.
