Most gin-poles I've seen are dock-mounted, manual (hand winch) cranes used for stepping and unstepping masts from boats that pull up alongside.
Are you asking about a system to raise and lower your deck-stepped mast, by pivoting at the tabernacle? If so, most folks just use a spinnaker or whisker pole, or the boom, as the offset.
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Pacific Seacraft Crealock 31 #62
NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT