I would imagine using a gasoline tank for diesel wouldn't hurt it that much, as in the manual it says you may add gasoline in case of emergency. Diesel in a gasoline engine however, isn't as forgiving (blows god knows how many parts)
as for the tranny swap I have no clue, but I know my mechanic would. Its definitely possible to do the swap, maybe a few parts or whatnot. Don't forget to put in a new clutch while its out
jon