I'm currently buiding an "Rorty Dedion Axle" and the plans are great.

However, I just found out that the measuremet between the upper and lower trailing arm is 146 mm on Rortys plans. On my book chassie I have 110 mm between them.

I have looked at to the posibility to use 110 mm on the axle, but i'm afraid that it will be to narrow for the drive shaft to move with the suspension.

The other way is to make new 146 mm front mounts to the trailing arms.This will however make the car higher as i use the upper rear trailing arm bolt to mount the coilover. The car will be aprox 18 mm higher in the back

Does anyone has a suggestion how to do this?

Put a mount on the back of your axle brackets and slope the shock back to lose the height.

As it happens I am just going through exactly the same problem.

I have decided to put the trailing arm mounts in front of the dedion axle.
(In effect shortening trailing arms, but they no longer have to go around the drive shaft.

the shock mount then sits where the trailing arm mount should have been, this then strengthens the axle as it will be welded to the 4" tube and the 2.25" tube.
The shock will then be sloping backwards slighlty (I know that ideally the shocks should be orientated the other way, but if it works on the live axle than it should work on a dedion)

I ended up in mounting the traling arms on the back of the axle. I have to move the front trailing arms mount or make longer trailing arms.

Otherwise the wheelbase will be shorter.