Requirements:

Transport of Human Remains

1. Certified copy of Death certificate
2. Burial/Transit Permit
3. Passport or birth certificate of decedent
4. Embalmer's affidavit      
5. Letter of non-contagious disease from State or County Health Official (signed, notarized and authenticated by local County Clerk)
6. Funeral home letter stating: 1) only remains are inside the casket; 2) flight itinerary; 3) consignee's name, address, and telephone number;
7. No restrictions on type of Casket but a steel sealer is preferred
8. A new wood-bottom airtray

Consulates: http://www.state.gov/s/cpr/rls/fco/164201.htm#guatemala

Embassy: http://www.guatemala-embassy.org/