I have not heard of many using seacast. I don't know the weight nor the strength of it. Since you are in Fl, I would confer with Don @ "Hermco" in Jensen Beach or Mike @ Wildfire Marine in Stuart. These guys are the pros.
I see by your pictures that your fuel tank is aft of the console. I would suggest you invest in a Hermco full flotation bracket to handle the weight of your fuel, the four stroke you plan on using and people on board.
Notice how my '78cc sits in the water with a 250hp & the flotation bracket. I have 135gal of fuel but under the console not aft
