8 3/4 chunk question

Basically it's all about the pinion diameter. The 741 is the smallest, the 742 the next size up but and a machined cut on it, and the 489 is the biggest but has a tapered end on it and uses a crush sleeve but you can now over come this by using a solid sleeve on it which will make the 489 even stronger. Best bet would be to get your hands on the 742 or 489 (these two have the best selection of gears for them).