My idea for getting a custom frame built seems to be too difficult for frame builders to attempt. So instead I am thinking of modifying a Cromoly frame (Kona Sutra) I am wanting to know if the modifications are safe as it involves drilling into the frame.

I would need to enlarge 2 of the gas vent holes, one on the fork, and another on the chain stay, these two holes would need to be enlarged to 5mm (0.2in)

In addition to those two holes, a completely new hole would have to be drilled into the lower half of the steerer tube, again it would be 5mm (0.2in)

All of this is so I can internally route a dual strand 18 AWG cable from a SON28 hub to the front and rear lights, although 22 AWG is recommended for 6V 3W dynamos, with 18 AWG I will have less than <1% power loss through the cables.

I have attached a picture to help explain what I mean, aswell as some pictures from some one elses Di2 install.

From the SON28 Hub > Into the drilled out gas vent hole > through the fork leg > coming out of the crown (a hole for this already exists) > attaching to the front light.

From the front light > back into the crown and up the steerer tube > through a new drilled hole in the lower half of the steerer tube > excess wire will be looped in the empty space between the headtube and steerer tube (to allow the forks to turn) > through a hole in the head tube that goes into the down tube (this hole also already exists) > through the bottom bracket > into the chainstay > and out an enlarged gas vent hole, that I would need to drill out in the chainstay > up the rear rack to the rear light.