If your going to connect any of them back to back ( flywheel to flywheel ) & take the drive out of the center, one of the motors is going to require a rethink with regard to the chain/belt tensioners & valve train as its going to have to run backwards, the crankpin oil timing might also need to be changed along with piston offset etc.
Looked into coupling two pushrod 1.8L Subarus in this fashion many years ago with a view to kitplane use. Subaru is a relatively simple exercise in that the two block assys can be fitted to a single alloy plate at the sump face with a spacer of the reqd thickness between the two blocks to mount the gears/belts/whatever between, In this case the prop shaft would have been above the fwd crankcase. Nose to tail mounting would be a different deal, your asking the single front keyway & crank of the rear engine to do work it was never intended to do..
Looked into coupling two pushrod 1.8L Subarus in this fashion many years ago with a view to kitplane use. Subaru is a relatively simple exercise in that the two block assys can be fitted to a single alloy plate at the sump face with a spacer of the reqd thickness between the two blocks to mount the gears/belts/whatever between, In this case the prop shaft would have been above the fwd crankcase. Nose to tail mounting would be a different deal, your asking the single front keyway & crank of the rear engine to do work it was never intended to do..
