In the main, and discounting other possibly important alignments/interferences (pipes, controls, cases, etc), and presuming the frame/swing arm is not substantially different (meaning WIDE like for a much more modern bike) you will likely be well served to simply shift the engine over the 3/4" to keep the chain alignment. It may seem like a big offset, and it might be due to other factors (alignments/interferences), but discounting those, you will be ahead of the game in the long run. Most people are thinking of the weight of the engine being centered in the chassis as being critical, but it would have to be very substantially lopsided to be noticeable. I'd bet that few engines are centered up center of gravity wise in the chassis, certainly many are not even close. If your rear wheel is close to being appropriate for the engine (like what it was manufactured with) Line up the sprockets! The engine will be plenty close. From a broader perspective, Consider your chassis priorities: You would very much like to have your rear wheel aimed directly at your front wheel, or more precisely the contact patch of your front tire. You want this regardless of whether you are building a road racer or a chopper. That is going to dictate where the rear sprocket "aims". Put your drive sprocket in the bulls-eye, and your bike will drive just fine. It is also equally important that the engine is aligned parallel to the rear wheel when the rear wheel is aligned with the front tire contact patch. Otherwise you will have dreadful chain and drive sprocket wear issues. Don't try to make ANYTHING align with the frame! The frame simply connects the other parts that need to align to one another. On its own, the frame needs to have no alignment at all with anything except for practical assembly. It is the wheels that need to align, and the engine align with the wheels for drive line considerations. The frame itself could be obviously asymmetric or even single sided as long as it holds the other bits where they need to be. Weight wise, the engine would have to be offset enough to cause the bike to be noticeably leaned over to one side when going straight down the road in order to cause a noticeable effect. Turn in would be quick to one side and slow to the other. This effect is never discussed. Why? because it is mostly never there. The rider is so heavy,at the business end of the weight pendulum, and so infinitely adjustable that it overwhelms the comparatively small lack of weight symmetry in the rest of the bike. You will be the automatic perfect counterbalance for most any balance imperfection just by piloting your bike.