Does a second gen downpipe have to be modified to be put on a 1st gen?

 

I believe they are a pretty close fit.

Btw, I have a cat that looks just like the one in your avatar, thinking about naming her rotor, of course.

 

a cat named rotor... ummm no, just no

 

The 2.5" RB downpipe fits perfectly.The 3" RB pipe requires a little heating and a small push up to tuck well.Its easy though,the 3" is thin wall stainless,I bet even a propane torch would be enough to get it moved.If your talking stock downpipe/precat,then yes,that will fit too,no mods.
Heres my 3",it clears everything easily...

 

Well, Data already took the name Spot, so I'm running out of options.

 

mmm thats a great pic haha