Yes the CJ's use a stand alone solenoid. I'm not familiar with what you currently have on the YJ firewall, so I can't answer that question.
I can tell you how to wire the stand alone one.
Looking at this picture.
The black wire is a Dedicated ground to the solenoid. This isn't OEM I added it for a better ground.
The 2 large red wires. One of them comes straight from the battery and connects to one of the large lugs. You can use the YJ wire that goes from the battery to the starter for this. On CJ's the alternators' large red wire goes on the side the battery is connected to ( on the solenoid)
The other side,(large red wire )on the large lug goes to the starter.
The 2 smaller wires.
You should only need 1 wire, this will be the small wire that used to go to the YJ starter solenoid.
If when you buy the solenoid it has 2 small connections they should be marked with a I and a S, You will use the one marked with the S. ( start) the I terminal only has power with the key in the start position.
I would also be a good idea to run a Dedicated ground to one of the bolts that hold the starter.