If the car has the factory installed carburetor on it, it will have:
'76-84 318
2-bbl – Carter BBD (either computer controlled or not)
4-bbl – Carter Thermoquad (TQ) - either computer controlled or not
'85-89 318
318 2-bbl – Holley 6280 (computer controlled).
4-bbl – GM Quadrajet (computer controlled)
The Holley 2280 (non-computer controlled) was used on a few older FMJ's due to supply problems – but not many.
If you live in a non emissions state (or city), a Chrysler design Holley 2280 will fit in place of your Holley 6280 if converting from computer control.
The same goes for replacing a Carter TQ or BBD computer controlled carburetor to a non-computer controlled carburetor without much difficulty (some TQ's have a different fuel line entry point).
A Carter BBD and Holley 2280/6280 can be interchanged but the fuel line needs minor rebending (not much) and a new choke thermostat (different length rods) and 2 vacuum lines are in a different position (depending on what year you are working on). If you have a vacuum diagram for both versions, then you are set.
Another method is to look at the carburetor (which means the air cleaner will need to be removed or at least set aside).
The TQ has an aluminum top and bottom. The middle section is black (plastic). The fuel line attaches to the rear.
The GM QJ is yellowish and fuel line attaches to the front. It will also have an attached electric choke.
The Carter BBD is aluminum (top, middle & bottom) with a yellow metal top plate (without squared corners) on top that looks like this.
The Holly 2280/6280 is also aluminum (top, middle & bottom) with a (yellow, black or white) metal top plate (with square corners) that looks like this.
At first glance, it is not easy to tell the BBD from the 2280/6280 apart.
If yours is computer controlled, there will be a black electrical connector, with six wires, going to the carburetor, with the electrical connector being about three-four inches to the front passenger side corner of the carburetor (and a bracket on carburetor that holds the carburetor side harness down).
If you still not sure which carburetor you have, then a picture would really help.
BudW