I'm running a '99 Explorer GT40P engine with no changes to the short block. Cam is a Comp Cams 35-510-8. Similar duration to stock but a decent jump in lift. Valve springs and such were provided by
Alex's Parts based on the cam specs. Roller rockers are Scorpion SCP-1021's. Those required new valve covers because they were too big for the stock units. The best option I could find to solve that problem was the Spectre 5018 polished aluminum set. I didn't like any of the cheap stamped covers I could find, and these were less than $100. Unfortunately, they're -REALLY- tall. I already had a 1" Edelbrock intake spacer installed, but even with that they barely fit under the GT40 upper intake. I had to tweak a few fittings for the upper to clear. The only thing that I haven't resolved is making the EGR tube from the OBX headers connect to the valve on the upper.
The system runs well. I'm just frustrated that I've still got a rough idle and 16-18 inches of intake vacuum. The cam specs don't really explain that. But there's certainly no shortage of power available.
There were all sorts of problems along the way, but those are a different story that could be avoided entirely by making sure the parts you're installing are actually what you ordered.