Asking for a friend, he's building a 'book' chassis with a 'rotary'? rear end using sierra drive shafts, do anyone know if thse need shortening ?? cheers,,,,

Depends on the track width he wants to end up with.

Sierra is a few inches wider than escort so either make the body fit and leave alone or shorten.

Most manufacturers build chassis to sierra track, if you build your own (including IRS) then its whatever you want.

NB/ one shaft is longer than the other so by swapping around you can get away with only shortening the long one.

Regards Mark

The Luego Locost IRS uses shortened drive shafts in a book width chassis