747-300 Exit Limit
Exit limit should be increased to 660 in accordance with the FAA type certificate document: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/b3bb8eb44b6d73748625804400536f22/$FILE/A20WE_Rev58.pdf
This makes sense as it is the same fuselage as the 747-400, with the same number and type of exits.