? 2.5 performance mods now / 3.4 later

[HB.]

I'm just trying to do some early planning so I don't waste money on parts I don't really need. I will be planning on doing the 3.4 conversion sometime in early '09, maybe even late '08 (seriously doubt it). My question is could I still purchase after market performance parts for my 2.5 engine, that will work with the 3.4? I was looking at some headers for my 2.5, but didn't know if it would mate with the 3.4 when I do the swap. I would also like to know if I can't do the headers, are there any other parts I can upgrade, ie. intake, exhaust etc etc, or should I just wait until after I do the conversion to do these after market upgrades?

Thanks in advance