A seven-digit army service number simply means that an individual enlisted voluntarily sometime prior to implementation of the Selective Service Act. Such numbers were assigned randomly. The Selective Service System assigned eight-digit numbers which readily identified an individual's component (Regular Army, National Guard, Army of the United States), the military district where he entered service and other info. Perhaps the following associations can assist in locating your man (or his next of kin).
American Defenders of Bataan 1231 Sweetwater-Vonore Road Sweetwater, Tennessee 37874-5945
American Ex-POW Association Post Office Box 523 West Sacramento, California 95691-0523
Battling Bastards of Bataan Association has a website that features a message board, monthly newsletter, etc.: