If Doc Brown took the DeLorean back to 1885, and the lightning strike blew out the time circuits...and Marty took the DeLorean back to 1885, and the gas tank got shot out by the Indians, but the time circuits still worked...why couldn't they use both DeLoreans (which would coexist in 1885) to make one fully functional DeLorean, instead of having to use the train? (I must have watched the whole trilogy about six times on Starz over the break...)