BTW, re: your research note on his page, many people who emigrated continued to have themselves called by their middle names. Americans are not that rigid with customs.
For example here, my great grandfather in the 1930 US Census:
https://www.familysearch.org/ark:/61903/1:1:XSPL-J8F
But when three names were required on a document, three names were recorded, such as here with his WWI draft registration:
https://www.familysearch.org/ark:/61903/1:1:K6DX-S7L
Of course this does not cover within the family, where he was certainly still called Gunnar.
I mention it not only because it is important to know so that folks don't go down the wrong genealogical path but also because it makes me very sad to think that you think Americans would force a name on someone. :(