Is this possible
 

Hi everyone, First post in here.
I bought My first diesel truck today, (i am working oversea, had a mate to pick it up for me).
Ram 2500 manual cummins with 140k miles on the clock Immaculate body, really cheap price( Transmission blown up on the ride home) previous owner advised me that the syncs needed to be changed.. paid 5k for it, i will deal with it, planning to rebuild or get a new Nv5600.

I live in a very miserable city Where NON STOCK EXHAUST IS PROHIBITED ******* Lame.
i want to reach 500 rwHP ( 150gph Lift pump +water fluel sep. , Dual disc clutch, 90 hp injector, aftermarket turbo havnt decided yet, smarty, studs air intake...)

i want to run stack exhaust but since i live in this wonderful city it would be a nightmare..
what i thought about is an exhaust diverter valve (such as http://www.summitracing.com/parts/qtp-qtec40cp ) before the Cat. and keeping the original exhaust as a quiet alternative. i know i will have some plumming to do.. (is there enough room , i am ready to cut and re weld the original exhaust if i have to).
my question is is it possible To run the truck with all the mods ( with a low power tune/ level 1 on the smarty (never use any kind of chip correct me if i am wrong) or i will get incredible EGT? What should i do? is this any possible or i need to cut down on the HP, Any tip?
Thanks you very much and i apologize for my terrible english.
Matt

I think the 03 came with a 4" If so just leave it alone your fine!

The 03 came with a 3.5" exhaust and no cat. If your going to start modding 4" is definitely a must. I wouldn't think you would have any issues with the law upgrading to 4" as long as you keep a muffler on it.