Looking for a new muffler, but not a whole system
 

I currently have the rear silencers removed and replaced with straight pipe on my P38. As for that, the exhaust system is original. I was hoping to replace the original muffler with something that would give me a better sounding vehicle. I have heard good things about the Magnaflow set, but I don't need the full system as I had planned on keeping everything else.

What would be some good options on a bolt-in replacement for the stock unit?

Additionally, are the pipes on something like the Magnaflow system any bigger than the stock pipes currently on the vehicle? If not, I could use my stock pipes with a new muffler and get the same sound. However, if they're bigger, how much of a difference will my existing pipes make?

The sound is ok right now, but I'm looking for a bit more of a low rumble and a bit more volume when I punch it. The existing setup also produces a bit of a tinny sound that I'd like to be rid of, but I fear that's my existing pipes rather than the muffler.

Anything?

You should stay with the stock size pipes, going larger is not necessary for our engine.
As for what muffler to use, go to a local muffler shop and see what they suggest for the sound you want.

You can get a flowmaster muffler. It's a deep sound and it's amazing to my ears haha. If you get it you have to buy the offset ones and the right length. I have a friend who has a straight pipe and it is too loud and sounds like a fart... literally. And I have multiple friends with flowmaster systems and they sound great and a few with just the muffler, it sounds great. The muffler itself is around $80 without shipping. There is also a Thrush brand one (I've seen $27-45) and it is cheaper and DOESN'T SOUND NEARLY AS GOOD, more of a hot rod sound. Flowmaster is the ultimate truck sound but it depends on preference. I know that the diameter of the muffler is 2.5" on my disco, and most things are the same on P38s and discos, but that's worth looking up in your car manual.

Flow master has a drone that is annoying on long trips it never falls off.
Go with the Magna flow it sounds great on acceleration and then you almost forget its there when you have the cruise control on! If you don't have money for whole system the just get the muffler changed and the remove resonator and weld in a tip on the end.