I recently purchased a 94 Ext. Cab 6.5l turbo/auto

Firstly i want to make sure that all 3/4ton diesels had the 4l80e, and the truck already has the cat removed and a 3inch pipe back to the muffler (a flowmaster) Will cutting the pipe pre muffler and turning it out the side be a rediculous increase in sound over a catless with a flowmaster? Thanks for the help guys!

One other thing. a conical racing style filter, is it safe to run without an air box?