Side saddle = engine installed in stock passenger seat area.
However their 450 subframe is or may be adapted to a 451, the engine intrudes significantly into the passenger compartment.
I just don't think the performance is there, relative to the cost involved. When I have a passenger in the Radical, bringing it to about 1500 lbs, the thing is just lethargic. And that's when you're already in the powerband at 8-10.5K.