+1 you'll need a winch to adjust them, and the farther back onthe boat you can anchor the better but have seen them much closer to the mast and they still work ok.
SK78 Would be my #1 choice, add some cover and you're good to go. A 4:1 puchase will be plenty with a winch. V-100 would be another good choice or endurabraid. Depending on how long the standing part is, you shouldn't need too much line.
See the white line coming from the two blocked backstay:
Sorry for the big picture.
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