ive just fitted an echo sl to my 170mm's about half hour ago with a tarty brand bashguard + a trial tech freewheel spacer, the bash and spacer are probably 5 or 6mm and the echo went on lovely. if the threads are shorter on the 160/165's it would go on but just wouldnt be as strong, remeber under pressure the freewheel would try and twist off the threads wereas if it is screwed right on there is no leverage when it tries to twist. realy its a case of do you want to risk it.
possible outcomes
*it all works and your good!
*your hurt yourself when the freewheel pulls off at the top of a 15 ft wall + you will need a new crank arm and possibly freewheel + any other parts that get damaged in the fall! lol
:) :)