Hi,
I bought 4 new 6.5 inch speakers for my prelude, the previous owner took the rear speakers. I noticed that the rear speakers did not fit, I'm assuming that the rear speakers have pods, with 3 screws or something and then the speakers would connect to that... please let me know if this is correct. Also if that is correct, where could I find those pods

 

They do have "pods" Go look for some in a junk yard or on ebay.

 

My 5th gen has 6.5" round in the front and 6"x9"s in the rear. Are 4th gens' rears' different?

 

Yep. 4th gens are 6.5'' all around.

 

Rear speakers on a 4th Gen are 6.5's and yes they do go into a pod. You could just throw a sub in the trunk and leave the 2 rear speakers out, just make sure you have good speakers in the front.