if you could find a COMPLETE 69 harness you might have a chance. By that I mean underdash as well as all the engine bay. Then sit down with a 69 shop manual and act like it is a foreign harness, and justify each wire as you connect. Even then you'd need AC vs Non AC and so on and you'd need parts off the 67, like to adapt the neutral safety/ reverse stuff and so on.
Frankly with the advent of cheap digi cameras, this stuff is a LOT easier. I don't mean a smartphone. Look around C/L and buy yourself a basic DSLR. You can find older Canons for less than a hundred. I still have my old XT/ 350D it works fine. It's not worth 'anything.' You can find them as cheap as 75 bucks. I recently bought 2 more 7D's one a real beater, flash does not work, for 75, and the other for 150.