2001 mack rd with 8LL and convert to 18 speed rtlo 18918b

Asking for a friend. Anyone know what else needs to be done to convert from 8ll to rtlo 18918b? Everything should bolt up right? Should just need shortened drive shaft. Your input would be appreciated

 

Transmissions should be the same length. You can search that on eaton fuller or RoadRanger ratios ( some thing like that ) . It also lists lengths. Yoke length, joint size, speedo and where the shiftie thing goes maybe different. Some have different ends on the bottom of the shift lever and of course the shift knob.