would like to find obituary or newspaper articles on preston r.
twitchell killed on oct 23 1891.  he worked for the mexican central
railroad  as a foreman in the repair shop.

I found a 1850 Census report for a "Preston Twitchel", 11-year-old
male living in Oxford county, Maine. Is this likely to be your man?
Was he born in 1838/1839? Are you certain of the spelling of the
surname?

The 1850 Oxford county census page:
http://www.rootsweb.com/~cenfiles/me/oxford/1850/bethel/pg031-1.txt

yes this is the preston twitchell.  he moved to salt lake city after
the war with a land grant.  he worked for the mexican central
railroad.  he was a forman in the repair shop.  he was killed oct
23,1891 i can't find were.  think he was buried in miamiville cemetery
near cincinnati.  i can not find any obituary or write up about his
dead.  his wife lived in cincinnati and recieved a war penison.