There is "stock height" and then there is "stock" and they are not always the same.
Stock height can be had with multiple design criteria to still fall at the stock original ride height. These could have any number of individual leaves to make up the pack.
A stock spring pack would look and (hopefully!) perform the same as original, with either the 5-leaf or 6-leaf designs. Those would include the lower "overload spring" in those leaf counts. The overload being the bottom leaf, which is usually much thicker and flatter and not in contact with the rest of the pack until a heavier load is added to the truck.
There are some advantages to both, but I think most here would recommend the more modern design which is the 8, 9, or 10-leaf pack with the thinner leaves and a flatter arch for a better street ride. Perhaps losing a little load capacity, but whether that's a bad thing or not would depend on how often you drive it on the street empty vs how often you load it up or tow a trailer with your Bronco.
If you're in a hurry you'd need to go with what's available on the shelf. If you can wait that four weeks though, the Duff springs that Mike mentioned might be the way to go. They might be able to give you exactly what you want within reason. Worth a phone call or discussion here at the very least.
All depends on what you want to end up with. From your first post I would make sure to ask Mike if they have a way to create a 2.5" lift out of their stock height special order springs without too much drama.
If not, or if it's more trouble than it seems to be worth, I'd agree with the others to get a 2.5" pack right off the bat.
Hmm, to that way of thinking... You could purchase a 2.5" spring and remove two or three leaves to get the height lower. Then add them back in when you're ready to lift.
As long as you're not running a heavy rig or towing with it, this could work out well.
An added cost would come from the front springs of course, where you'd be buying stock height springs first, then another set for the 2.5" lift later. Unless you're thinking of keeping with the original springs in there now in the front? If so I would verify they have not sagged.
When you next have a chance. take a tape measure under the truck with your and measure between the top of the axle tubes and the bottom of the frame rails. If you are close to 7" in the front and 6" in the rear, then you're still very close to it's original height.
Good luck!
Paul