15 - 25mm. Ive got 20mm clearance in my driveshaft.
ATL driveshaft balacing and shortning are really good/helpful. They in hamilton
What good practice to do is to measure from the SEAL in the gearbox to the front flange on the diff. Make your own mesaurement but give this measurement to the driveshaft guys and they will tell you what it should be
Mike