Carburetor Identification

I'm having some trouble identifying these carburetors on my mom's MGB. It's a 79-80 year I think. She had a swap done with an MG motor that had a dual carb setup. One, if not both, needs a rebuild (I think the mechanic said the float valve was bent or something to that effect) and I need to know what model it is before I buy the rebuild kit. I see it says SU carb on it, but are there different variations of the SU carb or just one? (See picutres) And would a rebuild be the best, most cost-efficient way to go? Also, I wanted to know what the white handle is by the steering wheel. (see picture) Thanks is advance.
http://i8.photobucket.com/albums/a37/kurtsbleached/CARB3.jpg
http://i8.photobucket.com/albums/a37/kurtsbleached/CARB2.jpg
http://i8.photobucket.com/albums/a37/kurtsbleached/CARB1.jpg
http://i8.photobucket.com/albums/a37/kurtsbleached/Weirdthingy.jpg

The handle is for the vent. If you follow the handle you will see it connected to a metal flap. If you don't have one already, you should get a Bently repair manual. The repair manual includes a copy of the owner's manual.

The carbs are SU HS-4. There are sveral models of HS-4, newer 68-71 HS-4 used spring loaded metering needles, earliers cars used fixed metering needles. Other than needles, HS-4 parts should interchange.

Clifton