What carb is this? What are my options?

I would not put headers on a 273, 2bbl engine, for street use.

Dual exhaust off the stock exhaust manifolds,
Will wake that engine up a Lot.

Headers that fit the Early Abody are expensive.

1967 and newer Abody headers that are cheaper will not work,
the engine bay is too narrow.

The stock 2bbl cam is not 4bbl friendly.

If you really just HAVE to have a 4bbl, you better find out which year
heads are on the engine you have; 1964-65 have smaller sized bolts,
to hold the intake onto the heads.Those 2 year only intakes are not easy to find.

If your lucky and have 1966 and newer heads, get an LD4B,
or factory iron intake.Use a 500 cfm Edelbrock carb.

You can listen to my dual exhaust off the stock exhaust manifolds.

http://www.youtube.com/watch?v=Ud8mci4rjFU