Having just finished the calculations on a tabernacle, I can tell you the loads are huge and the metal assembly on the NIS designs would be typical of what's required, to keep the assembly reasonably light, yet strong enough to get the job done.
A mizzen that far forward in the cockpit means the back wind from it will always be going down your collar, which is annoying to say the least. It'll also make sure that any and all water that may splash up from the bow or sides, as you slog along will be blown on you. Then there's the getting in and out of the cabin thing as you dance with the stick. It can be done, but it's not the way I'd approach it.
Attached is a drawing of the ketch I just did the tabernacle calculations on. The main is stayed, but rotates. the mizzen is free standing and fully rotates. As you can see the mizzen is in a much better location, out of the cockpit so back wind and head bonking aren't issues anymore. The mizzen is intentionally moved aft, for separation from the main, which gives her a yawl like look. The main boom is well clear of the cockpit and when folded down, only sticks out past the back of the boat about 4' (1.2 m), which is pretty acceptable to most for towing. The tabernacle and related elements are the heaviest and stiffest portions of the boat. There are many interesting features about this custom design, but this maybe isn't the place to discuss them.