Wow.. I did all that and more and never achieved that dramatic of a result with any of my vans. Which is of course why I kept spending money buying and adding all those parts listed above! Then after it was all said and done I really wished I'd have just put in a bone stock LS motor and been done with it all.
I would advise him to add a custom y-pipe as well. Think I still have the one that came out of my Safari and it is one of the most horrible production y's I have ever laid eyes on(which is why I kept it in my scrap exhaust pipe pile). One of the y'd in legs inserted into the larger main pipe overshot the other legged in pipe so severely that it actually shrouded/impeded its flow a great deal and you'd easily cut your finger if blindly sliding it in there to feel the transition. Granted these are lower rpm motors.. but every little bit helps.