Are you planning to keep the rear fork attached to the transmission? Not sure where you will hide the shock and have enough space. Quick thinking seem like a short fulcrum and will need a very high spring weight.
Also curious about the added wear on the rear mount as the single shock will not give much in the way of added support as the two external shocks do provide some. Especially if in a single shock low pivot point. Makes for a long pivot advantage from the wheel to fulcrum. But maybe you have all that figured out.
Enjoy the project, will be cool to see the progress.