Once upon a time I ran a rigging and weight testing shop. When we tested shackles with pins or any kind of bar shaped item, the pull was always placed in the center of the bar or beam while the support was placed at each end.
If you have a three inch receiver and place a pin through it that is rated at 10,000 lbs., you should be able to put a strap around the center of that pin and pull 10,000 lbs.
Inserts would make no difference. The difference in weight rating associated with the 2" drawbar vs. 3" drawbar is going to be determined by the weight rating of the drawbar, which you would expect to decrease. However, a hollow 3" bar would be rated much lower than a solid 2" bar.

 

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I'd use Flex-Seal.

I think the 3" receiver was a solution in search of a problem.

 

I have bigger ***** than that!

They are 2-5/16'...the draw bars are 2".