http://www.nps.gov/fopu/parknews/immortal-600-living-history-event.htm
The site above says 43 died: 13 at Ft. Pulaski, 5 at Hilton Head and 25 after the return to Ft. Delaware. This does not count the three who died on Morris Island and were buried there. According to Ogden Murray’s book, they were:
W. P. Callahan Lieut., 25th Tenn. Infantry Died Sept. 26, 1864
Frank P. Peake Lieut., Bryn Artillary Died Oct. 2, 1864
J.C.C. Cowper Lieut., 33rd N.C. Infantry Died Oct. 15, 1864
Capt. Samuel J. Johnson (25th Tenn Inf) kept a record that showed these same three officers, with the additional information of the causes of death:
Callahan: Diarrhea; Peake: Dysentery; Cowper: “of an old wound”
Also, Johnson lists Peake’s unit as “Burn’s Artillery” and Cowper’s unit “25th NC Inf)”
However, Mauriel Joslyn’s book, Immortal Captives, lists Cowper’s unit as 33rd NC Infantry.
Also, Joslyn’s book lists Peake’s unit as Byrne’s Company, Kentucky Horse Artillery
Joslyn's "Biographical Roster of the Immortal 600" contains information on the deaths at Hilton Head.