Yes, there will be issues due to the different size balancers. The 69 balancer is larger in diameter so the timing scale on the timing cover is farther back. So if you still have the 67 balancer with the 69 cover, it may be tough to read.
Go to this page, a little more than half way down, and there are pics of the different timing covers. You're right. Some of them don't have timing scales. So there may be a separate scale you need to add.
