Help needed identifying Welsh/US casualty

[Hywyn]

I wonder if anyone competent in searching US casualties could help me with this one please.

Newspaper article (Carnarvon, North Wales) dated 3/9/1918 states

"Pte R H Williams, son of Mrs Williams, 1 Church Street has been killed in the war. He was 30 years old. Eight years ago he emigrated to Bute, Montana and he had enlisted in the American Army"

I think he may be the following on a local gravestone whom I have not yet been able to identify

"Gravestone ..... commemorates Robert H Williams killed in action July 30th 1918 aged 30 years and buried at the Somme.

Any help in identifying him would be appreciated