This topic has been the most interesting subject to me the past yr and i have read alot on it and talk regularly with 2 old timers who line breed very tight with outstanding results! I think your on the right track as you already know, I would continue to tighten it up with every cross you do. Seems to be the best way to stay in good dogs and not luck across them to me.
That's why the next cross will be Tweety to a direct son.

Then we will have plenty to work with from there on out.