First, has the truck been displaying any issues as of late? A drastic change in gas mileage, idling high, a check engine light?
Ford began using those composite intake manifolds in the early 90s. The "early" runs are notorious for experiencing failure. If you decide to replace the manifold, I highly recommend purchasing a Dorman aftermarket unit as they have revised the design with greatly improved reliability.
One possibility is that the first "stall" that you experienced while running the AC was the manifold initially cracking. As a result, an influx of unmetered air could have entered the engine creating a lean condition, resulting in ignition failure and thus the "stall". When you re-started the vehicle after the crack occurred, the engine was most likely operating under a very lean condition. Typically all air that enters your engine passes through (and is metered by) the Mass Air Flow sensor located just upstream from the air filter box. The MAF sends a signal to the ECU, which determines the proper air / fuel ratio. The unmetered air that entered through the crack causing the lean condition most likely resulted in a misfire scenario in the form of a loud backfire, (combustion when an intake valve or valves were open) allowing the flame front to travel backward through the lower and upper intake manifolds. Sadly, the weak point of that intake system is the upper intake, so the backfire would have cracked the already failed manifold even further. This scenario does explain the smoke coming from under the hood as well.
If this first scenario is indeed what happened, then most likely no damage occurred to anything other than the upper intake manifold itself. On a Taurus or Sable, this is not a difficult repair, however the restricted engine compartment of the Windstar makes it a bit more of a PITA.
Another scenario, albeit less probable, is some sort of ignition timing failure. "Timing" so to speak is the harmony of the rotating mass of the engine (crankshaft, connecting rods, pistons, camshafts) and the associated valvetrain components in conjunction with fuel delivery. When an engine is properly timed, the ignition process occurs slightly before the maximum excursion of a piston in a cylinder when undergoing a combustion stroke. This is phrased as "X degrees before top dead center". If you have some sort of issue that resulted in a timing error, then a backfire is certainly possible. Again, if a backfire occurs, the weak spot in the top end of your engine is the upper intake manifold, thus explaining the crack. What could cause an ignition timing failure? That depends on whether or not your Windstar is distributorless or has a distributor. What year is this thing?
It's most likely the first scenario. Chances are you'll bolt a new upper intake on and it'll fire right up, assuming proper installation.
If it is the second scenario, then you would have most likely been experiencing a poorly running engine beforehand.
Either way, you did not crack the engine block. I've never seen an engine that isn't highly modified with a "cracked" engine block.
