*87 YJ hardtop 258 w/4.0 head, Crane 260, Clifford intake, Holley 390, Borla header.*
You should put this at the top of your post so I don't have to go chase it down...
You haven't described under what circumstances you are having this 'Problem' or even what the 'Problem' is...
We don't know if the vehicle is spark knocking, missing, bogging (falling on it's face when trying to accelerate), cutting out before taking off when you depress the throttle, or what's going on.
You just said you have a 'Problem' between 1.5K & 2K....
Just between me and you, I'd think that it's a fuel problem at just off idle way before I'd think a stock distributor is the problem...
At the RPM you quoted as the problem, (1,500 to 2,000 RPM), I'd come more of thinking that you are having a transition problem between the high idle circuit and the main fuel circuit in your new Holley... (especially with headers...)
But that's just me...
What have you done to your distributor/ ignition so far?
If you haven't already upgraded the ignition to the 'TeamRush' ignition upgrade, you may be experiencing cross fire in the cap.
Starting with the larger cap and rotor, better plug wires, and a coil that is controllable is a good start.
You need to move your vacuum advance source from baseplate or manifold vacuum to a 'Spark Ported' vacuum source.
(The call it 'Spark Ported' for a reason...)
You need to check to see if you have the type of vacuum advance that has a limiting screw built in to the diaphragm assembly.
You may be able to limit total vacuum advance like that.
(Look in the nipple where the vacuum hose connects, there will be a screw through the vacuum diaphragm that limits travel of the diaphragm.)
Your adjustment may already be built in...
More than likely, you need one heavy (Jeep factory heavy, not tune up kit heavy) and one medium spring.
Jeep used a heavier spring than Ford did for passenger vehicles.
(The only time I've seen a spring that heavy on a Ford vehicle was on farm trucks.)
If your distributor has been apart, and the 'mechanic' didn't know exactly what he was doing, you may be getting way too much mechanical advance.
The advance head has two limiting slots in it, (See Graphic).
One is moderate, while the other is the built in 'Lets Go Racing' advance slot.
You will find a plastic 'Bump Stop' around the advance slot limiter arm.
(If you find you don't have one, at least use a nylon wire tie to replace the bump stop)
Using a piece of thick rubber tubing (like vacuum line) over the limiter arm will decrease the total centrifugal timing by just 3 to 5 degrees.
You can also (and I'm not recommending this) drill holes in the advance weights.
Lighter weights take more RPM to extend them with the same spring pressure.
This is a last resort when you can't time the advance any other way.