Hello, I'm buying new blocking for my running rigging, when I bought the boat (sloop rig 25') the blocks i.e. pulleys were missing. I haven't sailed since 1986 and I don't own that boat any longer. Am I correct in assuming that I need a block attached to the boom and one attached to the boat for the mainsheet? Also, a block attached to the boom and mast for the boom vang. If this is correct than I would need four blocks in total? Is this correct and is there specific blocks I need for each function and or position? Please help, and constructive criticism is appreciated, thank you.