Is this exhaust setup possible

[GONE1445]

I got this off of areo turbine exhaust's web site

Hi, I did a neat system this morning. About 18 months ago, I put on a 430402 Flow Master muffler and 2 1/2 tail pipes with 3 1/2 x 24 chrome tips. He loved that system but wanted to change the tips. He said the truck seemed to be restricted over 100 mph its a 2003 dodge extended cab, with a hemi. We scrapped the whole system. I cut off the factory cat put a HI FLOW 3 1/2 cat, then a single straight 4" pipe to the 4040 aero turbine muffler. The 4" mandrel tail just over the rear into a custom 4" inlet dual 3" out mandrel Y. Then using only mandrel blend, built the tails pipes out the back with those big magna flow 35175 Tips polished S.S. It sounded awesome, the customer called me later and said it was just a little quieter in the cab then the flowmaster system was, but there was a marked difference in acceleration from about 40 mph to over 100 mph. He loved that it has a unique sound, not like the other dodge's on the road. He is going to post al these pictures (the ones I sent to you earlier) on a local Dodge Ram Club website some more for my company and yours. Thanks for all your assistance.

is that safe to run a 4" into dual 3" exhaust on a hemi all the duals i have seen are 2 1/2"