On my h25
My 1979 model has a wire cable fixed at the masthead with a fixed eye and at the boom end with a snap hook for easy removal. I do not know if this was factory or not but I changed that with a somewhat shortened topping lift wire cable to which (at the boom end) I attached a pulley arrangement allowing for some boom height adjustment. I noticed that two of the late 70 vintage h27s had a similar arrangement to this. Works well but a powervang probably would be the ideal answer.