They didn't ever produce a factory aluminum head for the production 5.0's. To see if they're GT40s (cast iron - like the Cobras and early Explorer/Mountaineers and pushrod Lightnings) look on the ends of the heads. If they have 3 parallel stripes (bars) cast into the end of the head, they're GT40s cast iron units.
I had a 94 Bronco a couple years ago. 93-96 were pretty much the same. Cast pistons, flat tappet hydraulic cam, E7 heads, cast iron manifolds, and the truck intake. If it was modified, you should follow the advice of the others. If you are 100% cirtain its stock then it has the E7 heads, same as the HO.