Originally Posted by 2door
Welcome to the community.
The reason Greg warns about a rear suspension bike is that as the rear wheel moves, up or down, that will loosen or tighten the engine drive chain.
Unless you want to make some sort of super responsive HD spring based tensioner or get your output gear in direct alignment with the pedal sprocket, your drive train will be constant source of frustration.
The best way I know is to jackshaft the engine over to the pedal side that is already designed to work with the soft tail and use it.
Might as well use gears that way too.
Though considerably more expensive, in a soft tail with center cavity intrusion an electric is ideal.
The same operation as a jackshaft just without the shaft as the motor output is right there.
Many options, just beware the issues with direct drive on a soft tail.