FPO, the 737 does not have internal IRU updating and is 0.10/GLS certified as standard equipment. The GPS receivers are part of the MMR, not part of the ADIRU. And one can see quite a bit of IRS run-off after a lengthy flight, just recently after a 6 hour sector had the IRS's around 2 to 3 NM off the FMC/GPS/radio position, and the ANP was still 0.02. There is no need for internal updating as the IRS is only used for its short term stability and the GPS provides long-term stability. Filtering based on that principle is done in the FMC.