O.K., I've not done a mast that size but just thinking about it, I wonder if you should measure from the mast hinge
location to the transom (assuming you will lower to the stern, i. e., hinge
is towards the rear), and compare that measurement to the half way point on the mast.
In other words, how far beyond the end of the boat will the balance point of the mast be. If the balance point is beyond the end of the boat, you must push down at the hinge
end hard enough to counterbalance the mast and relieve the pressure on the hinge
pin. That downward pressure will be added to the weight of the mast at the rear support point. Try to make sure that your support point is strong enough and that you are able to put enough downward force to balance the short end of the mast at the hinge. In other words, have help the first time.
I'm not being discouraging, I think it's a great idea. I just want it to work, and want you to be prepared. How will you support the mast when it comes down, will you be on land or water? Let us know how it goes!