I had the same idea, using 2 u-joints on each side. But that would change the overall length of the axles pretty good to get any angle.
And with your idea, would you really need 2 cv joints on each side? Since you are attaching the sprocket solidly anyways, couldn't the inside just be a straight shaft from the tranny into the sprocket (or just keep the one original cv joint by the tranny)? Make those chassis mounted bearings into bearings inside a rubber bushing and just have the new cv joint (actually would need to be a double offset joint) on the outer side handling a larger angle. Then you would just need one custom axle with a shorter middle shaft. Those aren't too hard to order (or make for the backyard machinist). I assume you don't plan on driving 120 mph in this thing.
And on the plus side, no engine moving required without the extra cv joint, if I am understanding what you are saying correctly.