you sure you don't mean 265/35/20 in the rear? 235/65/20 would have a hard time fitting on a jeep...

i'll just assume it was a typo... measure measure measure... compress the suspension using a jack to see how your tires go up into the wheel well.. i used putty once to measure the space left after compression, just put it on top of the tire and compress the suspension up, when it comes back down you'll have a good idea of space left on a full compression..