Its quite doable if good practise is observed.
I thought about that a lot when building the mongrel but ended
up wiring on the fly to my own specs externally in the end as I used more cable than I needed
for future projects.
I might still do it though
It looks like a CDI bike right? not that it matters really
I've stripped a few CX looms and found
much of the thickness of the CX harness is due to commoning of the
ground ( green) and live ( black) cables.
this can be dispensed with if you devise suitable alternatives and will cut down the
overall diameter and so the size of the hole needed
Lets say you drill a hole near the headstock for the harness
and start feeding rearward
I was goin to drill underneath at about the position of the tank lugs
you'll need an exit for the oil pressure and temp gauge wires midway
just above and forward of the carbs
so a 6/8mm hole ( with grommet) should do for that
the neutral wire can run all the way back.
I figured a 20mm max hole on the outer bend just above the airbox wouldnt compromise the strength
much and I could have run cables to the rear in the tubes as well if I had wanted to.
the airbox area is where the CDI, stator, brake lights etc meet the harness so connections
need to be done externally in that area.
You'll need to be prepared to hack the harness up, lay in good fresh cable, rejig connectors
and have a jolly good idea what your doing before you start.
"plan the work and work the plan" as they say
Sketching it out however roughly, would help it may get messy otherwise.
I have no wiring diagram for my bike but tend to memorise things like that
and use the Honda colour conventions anyway so its pretty simple to figure out
I added a TI ignition harness to a basic CDI harness with some 'extras'
It all works reliably but I do keep seeing things I'd like to alter and could simplify
if I hadnt added so much redundancy
I also dispensed with the ground point on the battery tray which is common rot point
and welded a threaded boss on the inner part of the frame near hwere the CDI used to be
and have a few earth cables commoned there.
My flasher units in this area as well.
the most busy part of the harness is up front.
Its not so easy to simplify here unless you start dumping things like indicators
so for me its a necessary evil.