S&S recommends keeping the motor above 2700 rpm on bikes. Most of the bikes come in at around 750lbs. The M3W starts at 1200 lbs. With the added weight I'd try to keep the motor above 3000 rpm just to be safe. You can feel the torque spikes until 3700 rpm then it smooths out. The torque peaks at around 3300 rpm? I don't think the Centa unit is robust enough. Many of the couplings like this are made for constant speed pumps and generators. This car clearly does not fall into that catagory. The transmission was made for a car that could go from 1000 to 7000 rpm. Our effective range is from 3000 to about 4700 rpm. There are gaps. So we have holes where you're lugging the motor or pushing the revs hard with some areas of sweet spots joining them. Then there is reverse! I just cracked the frame on my 2012 with the added brace. The motor is clearly too powerful for the frame and the Centa unit. Take care.
What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.