Re: Need some input
The roller acts as a tensioner and guide. Run it as close to the rear sprocket as possible, and lined up with the sprocket centerline. That will compensate for any chain misalignment and keep the chain from running off the lower edge of the sprocket.
I prefer to keep things simple so no tensioner would be nice. But you would need to keep all slack out of the chain and alignment then becomes critical.
Most people seem to be putting the sprocket dished out in order to gain more clearance between the tire and chain. When I measured everything, the best chain alignment was achieved by dishing in. The distance from the bike centerline out to the sprockets should be the same for the engine sprocket and rear wheel sprocket. There is just enough chain clearance for a 2.125 tire. A 1.75 tire would be better. If you need a little more clearance, it might be better to skew the front of the wheel slightly to the right. Just not so much that it interferes with the pedal side chain.