"I have done this on my own when I was younger, but this is not for the faint hearted!"
Well I am still pretty young (and foolish!)
"Another problem is that this position will raise the roof line by about 6".
If the mast
is stored on the cabin
roof, if it is stored in a cradle
to the side of the roof then it could still work.
"You will also have the mast
sticking out ahead and astern, and will need to remove the shrouds and backstays
This is true, I would have to be very careful when moving the boat in this state.
roof is I believe 7ft 5 inches on the 900 and 9m. If I can make a safe and over-engineered removable tabernacle then this could still work.
I could cut the tabernacle 3 inches from the deck
and weld a strong plate onto the square section that was left sticking out. this could be reinforced with strong lugs on each side.
I could then do the same to the top part of the tabernacle.
These two parts
could then be bolted together using eight strong self locking nuts.
Kind of like this, but stronger and more reinforced.