Driveshaft length??
http://www.moparts.org/Tech/Archive/axle/5.html
look like 2.26 inches...
you need to see what yoke you have on your driveshaft...and what yoke is on the 8 3/4
there is two sizes....7260 and 7280......you probably have the smaller 7260 yoke on your driveshaft...
there is a conversion U joint that lets you connect a 7260 yoke to a 7290 yoke...if needed...
or if the 8 3/4 has a 7260 on it....no conversion driveshaft is needed.