It has the stock L-48 w/automatic, which everyone knows is a dog of an engine. What options do I have to 'make it go faster'?
You are feeling the same way I did when I first got my car.
Everything is pretty much going to depend on what the e-check rules are for your area. If you can find a way to get yourself exempt from e-checks, then you have a plethora of options. If you need to maintain e-check, you really have few options.
WITH E-CHECK REQUIREMENTS
There's not a whole lot you'll be able to do to actually make a
noticeable seat-of-the-pants difference in the performance. Minor exhaust changes like a high flow cat and some performance exhaust. Since you already have the FM50's, you probably won't do much better in that area.
I'm not sure if there are any heads available that will still maintain e-check compliance. If there are, that
may give you a noticeable difference, but you're still limited by your OEM exhaust manifolds. The engine really can't breathe all that well to fully utilize a nice set of heads.
WITHOUT E-CHECK REQUIREMENTS
This is easy... cheapest and quickest way to noticeable performance is to get rid of all the emissions stuff on the engine. You can dump the single or dual intake snorkel setup and go to an open-element air cleaner. From there, put some headers on. That'll get ya started for pretty cheap and give you some better sound and performance.
That was my setup for a long time and I was (relatively) happy with it. After that, I just went right into a new crate engine. I didn't bother trying to build up an old, worn L48 engine. It sits on an engine stand in storage waiting to be sold to the first person to give me $350 for it.