Interior noise...and now the REAL challenge starts
I had the chance to compare a 1995 powerstroke to my 6.9, and I can tell you the powerstroke was louder. Both trucks were XLT's and both trucks had all their factory sound insulation in tact. Both trucks had properly functioning exhaust systems as well.
You're going to want some kind of mass loading on the interior metal to cut down on the noise. Firewall and foot-wells in particular (just like the factory equipped diesel trucks). I used a low cost product called "Frost King" and it works well but not quite as good as the Mass Loaded Vinyl and Jute Rubber that was used from factory. If you really want to kill the noise, you'll also need insulation inside the fenders and hood. That will prevent sound reflections from entering the cab, or passing through the windscreen.
When I put my truck back together, I was reluctant to reinstall the hood lining insulation because it wasn't very nice looking after 30 years. The added engine noise convinced me it was worth trying, and it was noticeable. In fact I may even attempt to somehow clean up the fender lining insulation and put that back in too. A lot of noise gets bounced around in the engine bay, so the more you can kill there, the more effective your cab insulation will be.
If you have a look at my resto-project, Page 10 and up deals with sound proofing:
https://www.oilburners.net/threads/tin-bashing.71759/page-10
With everything I did thus far, engine noise is comparable to stock. However wind noise was also cut down thanks to a combination of added roof lining, stiffeners and new weather seals. Engine noise may seem like a problem right now, but once you get that powerstroke/5speed combo up to speed (and it will accelerate effortlessly!), You'll likely find that wind noise is the most annoying beyond 70 MPH.