Bottom bracket help!

caveat:
i think what you're saying is that you're trying to change the bottom bracket on what i presume is an old bike from that 'cup and cone' style BB (the one pictured measuring 120mm?) to a more modern sealed cup BB?

yep ur exactly right, i do want to change from the cup and cone to sealed, and also yes the bike had two front cogs on it, which ive now reduced to one. so all in all should i be looking for 68 x 120 or something shorter because i'll only be using one front cog??

thanks for the help guys :D