What carb is this? What are my options?

That looks like a late 70's early 80's BBD. The older 273's had the intake bolts go straight down, your's are angled so its a 66 up motor. You can use an LD4B intake or other more modern LA type if you want. For headers consider spitfires, they are shorty types, and are relatively easy to install, you'll need someone to fab the down pipes, I mated mine to a TTI system. Do a search on this site for spitfires - they are made by a private individual Harold Johnson (I believe), and they cost around 250-300 a set. I have some on my 66 and like them.