Every thing yellow rose wrote is correct. I balanced engines for a living in my younger years. Also please note that the A833 for the A bodies also came with the small "904" spline too. It wasn't just the overdrive tranny that had it.
Buy everything you need for the 318 like it was a 340 internal balance (as long as it's a '68 318 motor). Those are the parts you need. 10.5 clutch set-up with a 130 tooth flywheel, small yoke tranny u-joints, of course.
Russ.