Josh-
I've done this swap many, many times.  Currently have one in a '59 Euro
(Semaphore) PU I sold to a friend of mine a few years back and also on a '61
Panel Van.  Just use the beam, tierods, balljoint arms of the '68 assembly,
then install the spindles, calipers, rotors, etc. from the '73.  Works fine
with the stock single-circuit cylinder, although upgrading to a '67 dual
circuit cylinder would of course be safer in the long run.  Servo isn't
really required as VW often sold disc brake systems on 71-79 models outside
of USA using a '70 Non Servo master cylinder (In fact my buddy that has the
'59 now also has a Euro '72 Single Cab PU w/stock 1600 upright and Non Servo
Disc Brakes.  It also has this neat Westfalia built extra wide flat bed
option too).  I like the 73-79 brakes better than the 71-72 because the pads
are thicker and last alot longer.  To retain the large wheel bolt pattern,
adaptors will have to be used (5-112 to 5-205).  Cost is about $125 to $135
off the top of my head.  Good luck with the changeover :)  Jim /
BusBoys@aol.com