I've listed the subtle differences I know of below:
     
     '68 front beam has shorter mounting holes centres then '69 
     (this is why you can bolt a '68 beam to a split window bus)
     
     '69 can have disc brakes on the front, '68 always has drums
     
     both have identical bodies from the outside, small rear lights etc.
     
     the rest you probably know.
     
     Lee.
     '64 samba
     ex '78 modified to look like '68
     l.s.griffiths@physics.salford.ac.uk