It's going to be a little ragged around the edges I think. I've inherited a lot of out-of-date slides which I've been able to bring up-to-date and flesh out, but there's still going to be a lot of chalk-and-talk, handwaving, and "why don't we just look at the code" by the end of the week.
To some extent I prefer busking it over having a formal presentation. It's more engaging to actually talk to your audience. It's easy to fall into lazy PowerPoint traps: reading out the slides, or sticking rigidly to the rails that the slides set out for you.
But to busk it successfully, you need two things: a strong and intimate knowledge of the subject material, and some structure (even if it's just in your head) to apply to the subject material so that it tells a cohesive story.
I have more material to cover, in more breadth and depth, than I have background knowledge. I shall be flying without wires in some of the sessions. Wish me luck.