The 1967 service manual says K20 is 150ft lbs. (1967, because that's what I had opened and didn't want to hunt the 1969 manual)
But, I just did my 1967 K20 and went with what the bolt manufacturer said, see here -
https://www.rockauto.com/en/moreinfo.php?pk=1392665
My bolts were 5/8 on the front and rear.