Have flown the 747 classic with the Delco, and Litton 72 and 92 and the tolerance on all three was 3+3T.
As far as the ADIRU, I was just trying to address the specific nav function and was not going to get into the PFD display since the original question was regarding the IRS/IRU functions.
I have also flown the Litton 92 with the FMS interface and again the tolerance we used was 3+3T. IIRC, there was even a GPS interface with the FMC.