I don't think you are looking for a needle in a haystack with the names from the memorial being accurate and can't be invented. You are lucky as most gravestones just list Ireland and occasionally a county. Shipping information can have a county but it is rare and more likely found in later records, you could try the Ellis Is.website, it is free. They may have gone home for a visit. Most US, UK, & CA census only give Ireland or Ireland Free State.
Most people would poopa the next suggestion but it does work and I have emails from people who tried and were successful.
The current telephone directory for Ireland/Westmeath shows
23 Higgins in Westmeath. 3 from Mullingar.
I would write to all three with all the information you have
as see if they can help you. If you can't find the website by googling, contact me at email@example.com
as I cannot put it on the message board as it is considered a commercial
website by rootsweb policy.