Before you try to tension the rigging on a 1972 Cheoy Lee (or any 1972 era boat for that matter) the first step is to check the chainplates where they pass through the deck. Since this is a wooden mast, you should also check the tangs on the mast and spreader attachments. These are probably close to shot by now and so you do not want to tension the rig without pulling them and checking them carefully. Also carefully check all of the swages and standing rigging wire since they may be at the end of their useful life as well.
If everything looks okay then sail the boat in a breeze to see whether she has a lot of weather or lee helm.
Once you are sure that you chainplates that withstand the increased loading, on a windless day, make sure that the boat is on her lines fore and aft and amidships. Then back off each of the shrouds so that the rig is fairly loose side to side. Take a light line up the mast on the mainmast from the main halyard and hang a weight on the end of the line near the deck. With the line tight measure the approximate rake and compare it to this sail plan. https://sailboatdata.com/sailboat/offshore-33-cheoy-lee
Do the same on the mizzen.
If there is more or less rake than shown, think about how the boat sailed and whether she is balanced or has weather or lee helm. If balanced then a prior owner probably changed the rake on purpose, if lee or weather helm, decide whether changing the rake to match the drawing will help or hurt. If the answer is 'help' then change the rake to match the drawing. If 'hurt' I probably would not change it until you live with the boat a while.
Rake is adjusted at the main mast backstay, triatic stay, mizzen lowers, and forestay (making sure that the fore and aft lower shrouds are slacked on both the mizzen and main mast.
Once rake is set, the next step is to center the masts athwartship. That is done by measuring precisely from the centerline of the forestay attachment at the deck to a point on a piece of tape on the outside of the rail of the boat abeam of the masts on either side of the boat. Using the line from the earlier exercise tie a bucket to the end of the line with heavy weight (water bottles) in it that hang below the rail. Wrap a piece of tape around the line and make a line where the tape aligns with the top of the railing at the mark from the bow. Move to the other side of the boat and check it there. If the marks align start tightening the upper shrouds on either side of the boat making sure that the masthead remains centered as you are tightening by measuring on both sides of the boat.
Now start to tighten the lowers, periodically checking that the mast remains straight fore and aft and athwartships. Stop when all of the lowers feel about as tight as the uppers. If this was a race boat, there would be known settings for rig tension. Needless to say there aren't known settings for this boat, so its largely an art. It can be helpful if you have access to a rig tensioning gauge, but it can be done by feel. Next start by tensioning the uppers a couple turns, and whatever number of turns that you take in the uppers take roughly half of those in the lowers. As you make adjustments check frequently that the mast is still straight fore and aft and amidships. When the uppers feel very tight, and the lowers feel tight, then you are done for now and time to go sailing in a stiff breeze.
Progressively load up the sails, overloading them a little on a beam reaching watching whether the leeward lower shrouds go slack. While the rig is heavily loaded, sight up the mast. It should appear to be straight in all directions or have the head sag just slightly off to leeward.
Lastly sight up the forestay and make sure that there isn't excessive forestay sag.
If the head is to windward, or the lower shrouds go slack, then the lowers need more tension. If the head sags off a lot, then the uppers need more tension. Make sure that you keep your adjustments symmetrical and remember that once the shrouds are tight each shroud only needs a small amount of additional tension since each half turn on one side results in a full turn when both sides are tensioned.
And that's all there is too it.