Would the length be the same, I thought the 8 3/4 took a shorter shaft than the smaller rearends[/QUOTE
It should be about 49 1/2" long, center to center on the u-joints. Speaking of which, you'll need to match those too depending on which pinion flange you have on the 8 3/4. You can always get a conversion joint, but, they're kind of hassle to find if you have one fail and need it right away. Since you are using a 904, I assume you are going to use a common slip yoke with the 2 1/8" u-joint. Hopefully you have the same size pinion flange connection so you can use a stock driveshaft and not have to make one. Just makes things easier. You can always shorten your old on too, but, you'll need a yoke (if your old one has the ball and trunion joint). If you have a mismatch on the u-joint size, that might the way to go, as you can have the 2 5/8" end welded on if needed.
