Technically you could use 68/73 cups in an 83mm shell and they wouldn’t need any spacers at all. If you have a closed BB shell, (i.e. intereupted seat tube) then you don’t actually need the central tube, which is there to stop crap falling down the seat tube from getting into the BB.
However 83mm cups have longer threads on them, so if you were a bit ‘heavy footed’ there is a danger that the 68/73 cups would would knacker the shell threads.
Also if you’re fitting a BB mounted chain device then there are not enough threads on the cup period and it’s a non starter.
