Link Procurement Tasks to deliver Just-In-Time without using up slack?

Brett --

I will be a bit of a "contrarion" on this situation.  In your example, the Predecessor (aka Driving task) is the Material Delivered task.  What I mean by this is that the Start date of the Material Delivered task determines the Finish date of the Order Materials task.  In a situation like this, in spite of the fact that some people recommend against this, I would recommend you use a Start to Finish dependency (that weird "backwards" dependency) with the Material Delivered task as the Predecessor and the Order Materials task as the Successor.

Yes, I know this this seems to be backwards scheduling, and yes, I know that some companies FORBID their PMs from using Start to Finish dependencies, but in your situation, I think this dependency accomplishes exactly what you want.  Using this dependency, you can determine the Start date of the Order Materials task, based on its Duration, and on the Start date of the Material Delivered task.  In the end, I am a pragmatist, breaking all the "rules" to give you a solution that actually works in your situation.  Hope this "contrarion" solution helps.  😁