[hatzie]

Excellent build. The attention to detail is stunning.

You should be able to make a custom U-joint intermediate shaft to mate the column to the steering box using $$$$ Borgeson parts or mixing the G and CK shafts. Judging from the quality of your build you have the skill and patience to do either.

The column wiring shouldn't be that difficult. I'd grab a CK column and lay them side by side.
If the turn, beam, cruise, and hazard multiswitch mounting screws aren't in different positions... You should be able to pull the multiswitch and slide the pigtail up through the G series column. Swap them with CK switches and pigtail that mate to your harness. Make sure the plastic pinch guard is located in the correct position and the wires run through it correctly.
The ignition and neutral safety are on the outside of the column so mating the newer switches should be a bracket fab job... No guarantees without looking at both.
The latest Schematics I have for G series vans is '88. The PDF is in my signature... they may help...