Whats different 88-89 and 90-91 CRX

I have an 88 CRX si. Bought it for 500. It has been rear ended. The bars that hold the bumper on are bent. Went to junkyard found 90 CRX with perferc back half. Bumper and brackets for 125. Then he tells me that it wont work on an 88. I say "Why?" He says, "I dont know but thats what it tells me".

So I ask a buddy of mine who has a 91 and he says that the body kits say if you have a 90 or 91 some modification for the back may be necessary. Okay what is different? Im thinking of getting the bumper anyway and say to hell with it. But if anyone knows I would sure appreciate it.