I put a 71 column in mine. I'm thinking that it should be the same as yours. If so, I think you are on track.
However I hesitate to make any specific comment on yours as I do not know what the 78 wiring schematic specifically looks like.
You should be able to go to your local library and get a copy of the van schematic.
For your backup light/neutral safety switch it should be a low cost item from any local parts store. With it in hand, it should be clear how it operates. Assuming it is the same as my 71, it is a slide switch operated from a tab inside the column (should attach on the shaft near the firewall.
Flasher knob, try looking at an online parts catalog (much like you find them for your 66) and see if they sell them seperatly. It may be that yours is broken off and can be simply replaced. Then again you may need to replace the whole turn signal switch.
Last question, not sure here. In mounting the column you don't have it too far back do you? I'm wondering if you mounted it so that the bolts lined up and it really needs to be farther forward?? Be sure that the backup light/neutral safety switch will attach at its location.
