With regard to the loading, besides on the cable and the stubby end of the lever, the load is no more than you would experience by lifting the mast yourself. 2" 1/8" wall square tubing would handle that with a huge margin of safety. The spreaders would be an issue and would have to be looked at closely but I think you'll find that with the lever positioned this way you will get much more height out of the system. The lower mast cradle will have to slide more on the mast - but what difference is a little more? You'll just have to put a roller on it anyway (a bow roller with side support). Just a thought.