[rpmerf]

You can look into the FAQs about disc brake conversions. I'll give a quick overview. The 1969 trucks came with drum brakes. Disc brakes started in 1971. There are a couple ways to convert.

Suspension parts that are different between 60-70 and 71-87
ball joints 71-87 are larger
tie rod ends (and adjuster) 71-87 are larger
center link 71-87 have larger tie rod holes. Be aware the idler arm size changed around 83.
spindle, hub, bearings, etc.

You can swap all of this from a 71-87 into your 60-70.

If you don't want to swap ball joints and tie rod ends, you can get conversion knuckles.

If you don't want to change your center link, you can get conversion adjusters that connect a 60-70 inner to a 71-87 outter.

So, where do you go from here. Since this was not done right, I would wonder about the ball joints. Check to make sure they fit in tight and are not falling out.

It sounds like you have your original center link (given that the 69 tie rod ends fit). You have 2 options -
Replace the center link, inners, and outers with 71-87 parts.
Get conversion sleeves and 71-87 outters.

Edit:
Now there is something with 6 lug vs 5 lug that I can't remember exactly. I have a C20, so it's all 8 lug. Hopefully someone can fill in what is going on there.