Hey Mike,
If you don't already have it, you should download the service manuals which can be found here;
http://www.tapeproject.com/smf/index.php/topic,1545.0.htmlThe wiring from the head switch should be done with shielded cables (ground the shield to the chassis at the output connectors end).
I've never done it with a 5050 but other members here have. I've done it with my Technics RS1500 and it wasn't too tough.
There may be some trial and error involved since the main pitfall is avoiding the hum induced from the motors (which is the reason for the shielding).
Other than that, you just need to keep the new cable out of the way of any moving parts (levers, linkages etc) and find a way to secure it there.
Hope this helps.