Beyond the headers, you need a new Y-pipe (crosses behind the transmission)... if you have any body/bed combo other than SC/SB, you will have room for an aftermarket hi-flow Cat and a muffler.
The DS O2 will need an extension cable.

SC/SB is very tight for length... you probably could squeeze in a Cat if you really had to.

Oh, and 4x4 is tight for front driveshaft clearance.

 

Though the LA headers have pretty much the same flange as the Magnums (they do have slight differences, but not significant), just compare the tube routing on the Pacesetter Magnums vs the LA headers, I dont see how they could possibly fit. It appears that they would run straight into the motor mounts and who knows what else. The only ones that looked like they might fit were Doug's LA engine swap headers, but they're waaaay expensive.