352029 would be his serial number. With his name, branch of service, rank, and serial number, you should be able to get his service record through the Nat'l Archives. Info on how to do so can be found at this address:
You can try to get his Individual Deceased Personnel File. Write to this address (including all pertinent info such as name, rank, etc) and be sure to cite the Freedom of Information Act in your request:
US Total Army Personnel Command Attn: TAPC-PAO (FOIA) 200 Stovall Street Alexandria, VA 22332-0404
(I know this says Army, but they also hold Marine Corps records for this period.)
I have also seen the following info posted online. I don't know if it is accurate.
"When a Marine dies, a Report of Casualty (DD1300) is issued by the military; in addition, a death certificate is issued by the State in which the death occurred. (When overseas, the death certificate is filed in the state of residency.) A Marine Corps officer notifies the next of kin in person. Upon written request, the next of kin can request all the paperwork filed by the United States Marine Corps in the course of the death investigation (all deaths are investigated as a routine procedure). As part of the investigation, the death certificate is requested by the investigating officer from the state and filed with the Marines Official Records. The references pertaining to this are 10 USC Section 2271, DODI 1300.9, and MCO P1741.8.
Copies of Marine Corps death certificates may be obtained from: Marine Corps Commandant Code M-HP-10 Headquarters Marine Corps 2 Navy Annex Washington DC 20380-1775 Phone 703-696-1177 Fax 703-696-2072"
If he was killed on Iwo Jima he was probably in the 3rd, 4th, or 5th Division (or a unit attahced to one of those divisions). His service record should tell you for sure what outfit he was in.