This is what 1977 masthead looks like.... as far as I know that's how it came from the factory. 2 internal jib halyards, 1 internal mainsail halyard. 1 static line for boom topping lift. 1 external spinnaker halyard block. Please note the width of the masthead sheaves when making a decision on halyard sizes. The original jib and mainsheet halyards were wire to rope, 1/8 wire - 3/8 rope. Finally, if you google "Catalina 27 diagrams" you'll find a lot of stuff. good luck. Oh, BTW a new masthead casting from catalinadirect.com (aftermarket vendor) runs about $384!!! So call Catalina Yachts parts dept. first, their prices are usually better.