Thought the poly mounts had the tube molded in?
The tube on the OEM style rubber mounts is there to prevent them from over compression when the bolts are torqued to spec. Which is why the tube/top hat style have to be cut down (all but the 2 forward ones).
Now, if you get an oem rubber set that doesn't have the sleeves or maybe a poly set that doesn't have the sleeve molded in, you can get a much better set at the junkyard. YJ's used a heavier metal and have a mushroom shaped top that fits perfectly over the top of the rubber mounts. Just can't remember if it is the front 4 or the rear 4 that fit. One has a smaller diameter tub than the other.
Again don't know if they would work with the poly mounts.
This is a YJ tube.
The left is a CJ body mount, right is a YJ. YJ rubber mounts don't fit the frame mounts on a CJ, center diameter is bigger on YJ.
The CJ tube cut down to the proper length.
When the "donut" is placed on the bottom it would look like this. The tube then keeps the "donut" from being compressed to far.
And not the best pic, was using a bolt that was too long so had too add washers, but shows where the tube stops the rubber bushings from over compressing. The poly bushings don't compress.
At any rate, hope this helps understand what the purpose of the tubes are.
Might want to verify if the tubes are or are not molded into the bushings. An old set of mine did. Probably why the center diameter is smaller.