Correct Length Throttle Cable

Your 2bbl. cable should be the same as a 4bbl. application- but this could vary depending on the throttle brackets that you use; i.e. factory 4bbl. brackets, modified 2bbl. brackets, aftermarket "fitzall" brackets, etc. and whether you're running a carb spacer...
You've got basically two choices for a factory style cable:
19":
More Information for PIONEER CA8417 (rockauto.com)
24":
More Information for ATP Y155 (rockauto.com)
More Information for PIONEER CA8418 (rockauto.com)
If you need something else, you're looking at a Lokar or clone.