Many thanks for your post to the message board and for sharing some of your Irish-Argentinian family information.
Yes, Longford and WestMeath were very popular areas from which the Irish emigrated from. In addition, there was also a merchant class from Limerick who went to Argentina as well in the late 1800s.
As a matter of interest, when I input both surnames into the John Grenham ancestors website, there are several parishes that come up that contain both surnames. This is a great clue in determining where your ancestors may have come from--particularly pre-Famine where due to lack of travel, many couples who married lived within 5 miles of one another.
Would you be willing to create a few Ancestor profiles of your Bannon and Gardiner ancestors on the XOChronicles feature which is located at the top of this page? These profiles will be of interest to any members who are also researching the same families and you may find that others will be willing to share and collaborate with you on your research.
If you have any questions about the above, please email me directly at: email@example.com.
All the best,